* fix compiling failure on cxx14

* fix compile failure when NCNN_PIXEL off

* do not export pixel api when NCNN_PIXEL off

* disable squeezenet test when NCNN_PIXEL off

* do not build ncnn2table and examples when NCNN_PIXEL off

* make cmakedefine header independent

* restore platform.h.in

Co-authored-by: nihui <shuizhuyuanluo@126.com>
Co-authored-by: nihuini <nihuini@tencent.com>

* fix cmake 3.5.1 config error

* fix ubuntu16.04 build error

* vulkan cmake export templete

* 1) vulkan cmake dependency export. 2) support opencv_world import. 3) add BUILD_WITH_STATIC_CRT option

* Threads dependency

* NCNN_BUILD_WITH_STATIC_CRT option

* we do not support cmake before version 3.15 for option NCNN_BUILD_WITH_STATIC_CRT

* add folder property for a better looking in visual studio or other property supported IDEs

* fix condition for not found protobuf

* 1. capitalize to lowercase
2. rename visual folder 'test' to 'tests'

* Update CMakeLists.txt

enable quant

* fix opencv compatibility issue with major higher than 2

* CMake improvement

* Fix bugs

* Fix typo

* Propagate vulkan dependency

* import vulkan

* add config files, now exported target cmake should be able to find packages

* Propagate no-rtti and no-exception

* Provide a option to control rtti and exception in mobile platform

* Make cmake clean

* Resolve conflicts

* Update CMake
PIE is propagated by INTERFACE_POSITION_INDEPENDENT_CODE

* Remove bad things

* initial the ncnn post training quantization tools

* clear some comments of tools

* fix the Travis ci compiler error