* set cmake NCNN_BUILD_TESTS default off and add -DNCNN_BUILD_TESTS=ON to ci

* fix cmake 3.5.1 config error

* fix ubuntu16.04 build error

* Update linux-x64-cpu-gcc.yml

* Update linux-x64-cpu-gcc.yml

* 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

* fix maxpool padding size

* restyle

* Update yolov4 example

Add streaming from OpenCV support.
Add time profiling support.
Improve error handling.

* [build] add toolchain file w/o stdcxx dependency

* [build] link m and gcc lib explicitly

* [ncnn] complete simple stl impl

* [ncnn] adapt for ncnn simplestl

* [test] adapt for ncnn simplestl

* [ncnn] fix missing algorithm and list when simplestl disabled

* [ncnn] fix guard for operator new and delete

* [style] fix the code style

* [build] fix build failed on darwin and emscripten

* [ci] do not import cxx to avoid operator conflict

* [ncnn] add temporary partial_sort impl using bubble sort

heap sort should be used for better perf.

* [ncnn] add std greater and less function

* [ncnn] fix placement new operator overload

* [ncnn] add operator delete with size info

* [build] disable exception, rtti, example and tools when simplestl on

* [build] add toolchain for arm simplestl

* [build] add toolchain for aarch64 simplestl

* [ncnn] move initializer to constructor

* [ncnn] use deteiled type instead of auto

* [ncnn] use plain lib name in target_link_libraries