* 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

* add relative README_CN.md;
* obtain time cost with op->forward().

* a portable thread class

* Update platform.h.in

* Update platform.h.in

* fix windows avx2 error in convolution_3x3.h and convolution_sgemm.h

* fix compatibility of avx2 under Linux and Windows

* Update CMakeLists.txt

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* Update convolution_3x3.h

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* Update convolution_sgemm.h

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* initial the ncnn post training quantization tools

* clear some comments of tools

* fix the Travis ci compiler error

* Implementation for hard sigmoid

Not yet tested.

* Resolve requests

* optimize conv sgemm with sse

* Update convolution_x86.cpp

* add the "Tu Fa" conv sgemm fp32 with avx2 for x86

* add avx2 cmake option

* fix some bugs of avx2 pull request

* 1.fix pad tail bug in commit d1ea2a3 at pooling layer

* fix illegal memory access at conv layer of vulkan

fix illegal memory access at conv layer of vulkan when bias term is 0