* Add mips-mti compilation to github action

* Remove protobuf installation

* Add mips architecture optimization support

* Add mipsisa32r6 toolchain files

* Add AbsVal_mips layer

* Remove unused constructor override

* Keep the same programming style with upstream

* Add Bias_mips layer

* Add Clip_mips layer

* Update copyright header

* Add mips-mti-gnu compile to travis

* Add codescape mips toolchain config

* Update the toolchain comments

* Fix conflicts in travis config file

* Add travis status in README.md

* Fix warnings C4244, C4267 in src/layer/yolov3detectionoutput.cpp

C4244: '=': conversion from 'int' to 'float', possible loss of data
C4244: 'initializing': conversion from 'float' to 'int', possible loss of data
C4244: 'initializing': conversion from 'double' to 'float', possible loss of data
C4244: 'return': conversion from 'double' to 'float', possible loss of data
C4267: 'argument': conversion from 'size_t' to 'int', possible loss of data
C4267: 'initializing': conversion from 'size_t' to 'int', possible loss of data

* Fix warnings C4244, C4267 in src/layer/yolodetectionoutput.cpp

C4244: '=': conversion from 'int' to 'float', possible loss of data
C4244: 'initializing': conversion from 'float' to 'int', possible loss of data
C4244: 'initializing': conversion from 'double' to 'float', possible loss of data
C4244: 'return': conversion from 'double' to 'float', possible loss of data
C4267: 'argument': conversion from 'size_t' to 'int', possible loss of data
C4267: 'initializing': conversion from 'size_t' to 'int', possible loss of data

* Fix warning C4244 in src/layer/quantize.cpp

C4244: 'initializing': conversion from 'double' to 'int', possible loss of data

* Fix warnings C4244, C4267 in src/layer/detectionoutput.cpp

C4244: '=': conversion from 'int' to 'float', possible loss of data
C4244: 'initializing': conversion from 'double' to 'float', possible loss of data
C4267: 'argument': conversion from 'size_t' to 'int', possible loss of data
C4267: 'initializing': conversion from 'size_t' to 'int', possible loss of data

* Fix warning C4244 in src/layer/roipooling.cpp

C4244: 'initializing': conversion from 'double' to 'int', possible loss of data

* Fix warning C4244 in src/layer/sigmoid.cpp

C4244: '=': conversion from 'double' to 'float', possible loss of data

* Fix warning C4267 in src/layer/slice.cpp

C4267: '=': conversion from 'size_t' to 'int', possible loss of data
C4267: 'initializing': conversion from 'size_t' to 'int', possible loss of data

* Fix warning C4267 in src/layer/softmax.cpp

C4244: '=': conversion from 'double' to 'float', possible loss of data

* Fix warning C4244 in src/layer/interp.cpp

C4244: '=': conversion from 'float' to 'int', possible loss of data
C4244: 'initializing': conversion from 'double' to 'int', possible loss of data

* Fix warning C4244 in src/layer/instancenorm.cpp

C4244: 'initializing': conversion from 'double' to 'float', possible loss of data

* Fix warning C4244 in src/layer/deconvolutiondepthwise.cpp

C4244: '=': conversion from 'double' to 'float', possible loss of data

* Fix warning C4244 in src/layer/convolutiondepthwise.cpp

C4244: '=': conversion from 'double' to 'float', possible loss of data

* Fix warning C4244 in src/net.cpp

C4244: 'return': conversion from '__int64' to 'int', possible loss of data
C4267: 'argument': conversion from 'size_t' to 'int', possible loss of data
C4267: 'initializing': conversion from 'size_t' to 'int', possible loss of data
C4267: 'return': conversion from 'size_t' to 'int', possible loss of data

* Fix warning C4244 in src/layer/bnll.cpp

C4244: '=': conversion from 'double' to 'float', possible loss of data

* Fix warning C4267 in src/layer/concat.cpp

C4267: 'initializing': conversion from 'size_t' to 'int', possible loss of data

* Fix warning C4267 in tools/mxnet/mxnet2ncnn.cpp

C4244: 'initializing': conversion from 'double' to 'float', possible loss of data
C4267: '=': conversion from 'size_t' to 'int', possible loss of data
C4267: 'initializing': conversion from 'size_t' to 'int', possible loss of data
C4305: 'initializing': truncation from 'double' to 'float'

* add assembly gemm

* m1/m2/m4 assembler-local label

* clean useless code

* Update gemm_symm_int8.h

add license

* Downgrade minimum cmake required to 2.8

In some embedded system, the cmake version is still 2.8.x. So use
SET instead of APPEND to adapt to more envir.

* Set cmake minimum required version to 2.8.12

* Adapt for cmake 2.8.12 using target_compile_options instead of feature

* Fix openmp compiling error on cmake 2.8.12

std::{unary|binary}_function<> are deprecated in C++11 and removed in C++17.

Actually, these were unnecessary in general. In the C++98/03 era, many user-
defined function object classes derived from these base classes in an attempt
to imitate STL conventions. However, STL containers and algorithms have never
required such inheritance (or the typedefs that they provide). Only the
function object adaptors (like bind1st()) needed such typedefs. Currently,
there are no uses of function object adapters in our codebase, so we can
eliminate the inheritance completely.

* Fix warning C4244 in src/layer/normalize.cpp

C4244: '=': conversion from 'double' to 'float', possible loss of data

* Fix warning C4244 in src/layer/requantize.cpp

C4244: 'initializing': conversion from 'double' to 'int', possible loss of data

* Fix warning C4244 in src/mat_pixel_resize.cpp

C4244: '=': conversion from 'double' to 'int', possible loss of data

* Fix warning C4244 in src/mat_pixel.cpp

C4244: '=': conversion from 'int' to 'float', possible loss of data

* Fix warning C4267 in src/modelbin.cpp

C4267: 'initializing': conversion from 'size_t' to 'int', possible loss of data

* Fix warning C4244 in src/layer/batchnorm.cpp

C4244: 'initializing': conversion from 'double' to 'float',
    possible loss of data

* Fix warning C4244 in src/layer/padding.cpp

C4244: 'argument': conversion from 'const float' to 'T', possible loss of data

* Fix warning C4244 in src/layer/priorbox.cpp

C4244: '=': conversion from 'double' to 'float',
    possible loss of data
C4244: 'initializing': conversion from 'double' to 'float',
    possible loss of data

* Change DataReader::read()'s signature to fix warning C4267

This CL fixes lots of warning "C4267: 'initializing': conversion from
'size_t' to 'int'" in our codebase by matching DataReader::read()'s
signature to fread().

* Fix warnings C4244 and C4267 in tools/ncnnoptimize.cpp

C4244: 'initializing': conversion from 'double' to 'float',
    possible loss of data
C4267: 'initializing': conversion from 'size_t' to 'int',
    possible loss of data

* Fix warning C4244 in src\layer\selu.cpp

C4244: '=': conversion from 'double' to 'float', possible loss of data

* Fix warning C4244 in src\layer\cast.cpp

C4244: '=': conversion from 'double' to 'float', possible loss of data
C4244: 'return': conversion from 'float' to 'signed char', possible loss of data

* Fix warning C4244 in src\layer\psroipooling.cpp

C4244: 'initializing': conversion from 'double' to 'float',
    possible loss of data
C4244: 'initializing': conversion from 'double' to 'int',
    possible loss of data

* fix compile error of yolov3detectionoutput layer

* fix ncnn2table coredump when [Input] layer not found in ncnn.param