Allow forcing a clean build and/or cleaning build dir

[matthijskooijman]

Bug Report

Current behavior

Currently, if an existing build dir is present, it is always used by arduino-cli compile

Expected behavior

It would be nice if there was a arduino-cli compile --clean option that would force a clean build (similar to what happens when the compilation options change, but this should probably also prevent using a precompiled core).

Additionally, an option to clean up the build directory would be nice. At first glance arduino-cli cache clean might do this, but the --help output does not specify what it cleans exactly, cache clean -v does not show what is removed either, and a quick test suggests that it does not clean the build directory.

Environment

• CLI version (output of arduino-cli version): Current git master be39aa9 (arduino-cli version did not output anything meaningful)
• OS and platform: Linux