ESP32

add esp32.toolchain.cmake, update esp32 docs and ic #18

	name: ESP32
	on:
	push:
	branches: [master]
	paths:
	- '.github/workflows/esp32.yml'
	- 'CMakeLists.txt'
	- 'cmake/**'
	- 'src/*'
	- 'src/layer/*'
	- 'src/layer/x86/**'
	- 'src/layer/vulkan/**'
	- 'tests/**'
	pull_request:
	branches: [master]
	paths:
	- '.github/workflows/esp32.yml'
	- 'CMakeLists.txt'
	- 'cmake/**'
	- 'src/*'
	- 'src/layer/*'
	- 'src/layer/x86/**'
	- 'src/layer/vulkan/**'
	- 'tests/**'

	concurrency:
	group: esp32-${{ github.ref }}
	cancel-in-progress: true

	permissions:
	contents: read

	jobs:
	build:
	name: ESP32
	runs-on: ubuntu-20.04

	steps:
	- uses: actions/checkout@v4
	with:
	submodules: true

	- name: Setup Python
	uses: actions/setup-python@v5
	with:
	python-version: '3.8'

	- name: Install dependencies
	run: \|
	sudo apt-get update
	sudo apt-get install -y cmake ninja-build ccache

	- name: Cache-ESP-IDF
	id: Cache-ESP-IDF
	uses: actions/cache@v2
	with:
	path: esp-idf-install
	key: esp-idf-${{ runner.os }}-install

	- name: Clone and Install ESP-IDF
	if: steps.Cache-ESP-IDF.outputs.cache-hit != 'true'
	run: \|
	git clone https://github.com/espressif/esp-idf
	cd esp-idf
	git submodule update --init --recursive
	./install.sh

	- name: Set environment and build NCNN for ESP32
	run: \|
	source esp-idf/export.sh
	echo "IDF_PATH=$IDF_PATH" >> $GITHUB_ENV
	echo "${IDF_PATH}/tools" >> $GITHUB_PATH
	echo "${IDF_PATH}/components" >> $GITHUB_PATH
	mkdir -p build-esp32 && cd build-esp32
	cmake -DCMAKE_TOOLCHAIN_FILE="../toolchains/esp32.toolchain.cmake" -DCMAKE_BUILD_TYPE=Release -DNCNN_BUILD_EXAMPLES=OFF ..
	make -j 4
	make install

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