Add docs subcommand with options:
--no-browser - Prints url for current documentation instead of opens browser with documentation
--language - Select documentation language
--starting-page - Choice section of documentation to open
--version - Choice version of esp-idf
--target - Choice model of your target
* add toolchain file
* add linux to preview targets
* add stub for dfu number in cmake
* excluded unity runner per default
* Added esp_attr.h and esp_partition.h linux stubs
* component.cmake check list for emptyness
* added switch for linux in unity cmake file
* Added Linux host example app