HOWTO: build on windows

[dpeddi]

The idf used by this project is a patched v3.3:

download https://dl.espressif.com/dl/esp32_win32_msys2_environment_and_toolchain-20190611.zip
unpack esp32_win32_msys2_environment_and_toolchain-20190611.zip
execute mingw32.exe

cd /opt
mv xtensa-esp32-elf xtensa-esp32-elf-8.2.0
wget https://dl.espressif.com/dl/xtensa-esp32-elf-win32-1.22.0-80-g6c4433a-5.2.0.zip 
unzip xtensa-esp32-elf-win32-1.22.0-80-g6c4433a-5.2.0.zip 
cd 
mkdir esp
git clone https://github.com/nullstalgia/esp-idf
export IDF_PATH=~/esp/esp-idf
export PATH="$IDF_PATH/tools:$PATH"
modify ~/esp/esp-idf/make/ldgen.mk
after
$(BUILD_DIR_BASE)/ldgen.section_infos: $(LDGEN_LIBRARIES) $(IDF_PATH)/make/ldgen.mk
	printf "$(foreach info,$(LDGEN_LIBRARIES),$(subst \,/,$(shell cygpath -w $(info)))\n)" > $(BUILD_DIR_BASE)/ldgen_libraries
add
$(BUILD_DIR_BASE)/ldgen_libraries: $(LDGEN_LIBRARIES) $(IDF_PATH)/make/ldgen.mk
	printf "$(foreach info,$(LDGEN_LIBRARIES),$(subst \,/,$(shell cygpath -w $(info)))\n)" > $(BUILD_DIR_BASE)/ldgen_libraries

git clone https://github.com/nullstalgia/UARTSwitchCon
cd UARTSwitchCon/ESP32/source/firmware
make
make flash ESPPORT=COM6
make monitor ESPPORT=COM6