* Update ncnn-android-scrfd link and demo picture

* Update ncnn-android-scrfd link and demo screenshot

Signed-off-by: Ndaquexian <daquexian566@gmail.com>

* Add [ MacOS ->  apple-cpu/apple-gpu] into supported platform matrix
 * Add [ mac ->  apple] into 'device support vulkan' list
Co-authored-by: Nmeow <826150766@qq.com>

* add vs2015 ci
* build x86 binary

* codecov for arm32 aarch64, vs2017 ci

* vs2017 default to x86 even on x64 host

Update README.md for Netron.app

* Add readme for keras2ncnn

* Add supported model variants

* Fix supported model variants

* Improve build instructions

* Merge Linux stuff into one section.
* Provide better info on dependencies
* Provide easier to use instruction for Debian / Ubuntu for native and cross-compile builds
* Capitalize Sentence and put proper punctation.
* Use backticks where appropiate
* Move Hisilicon instruction together with Arm crosscompiling
* Add information how to verify the Vulkan installation on Linux
* Change how to launch examples so it is easier (no copying needed or external resources)
* Add info about benchmark and how to test it on GPU or CPU
* Use `$(nproc)` where appropriate.
* Put some paths in quotes, in case they contain spaces or other weird characters (coma, semicolon, colon, etc).
* Remove some extremely obvious pieces that every developer usually knows.
* Use newer Vulkan SDK in instructions for Linux
* Get rid of `<ncnn-root-dir>`, and just use `ncnn`. It is what git clone does. And any developer will know how to change it if they choose to do it differently.

* Update README.md

* Update how-to-build.md
Co-authored-by: Nnihui <shuizhuyuanluo@126.com>

* runtime cpu dispatch

* force thread one

* disable openmp for coverage

* simplify test layer

* print NCNN_TARGET_ARCH

* less ci build variants

* weight fp16 storage option

* test convdw int8

* apple a12 a13

* ncnn_add_layer ncnn_add_shader cmake macro

* update readme: metion yolact, retinaface, etc

* update doc: add c/cpp/python for code region

* delete ccpp.yml

* add build.yml

* split all workflows

* delete single file defined workflows

* light up the building status matrix

* use short icons

* add actions to ios 32bit cpu position

* rename ios workflow file's name

* rename ios workflow name

* 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