Release 0.2.1-alpha.preview

This is mostly a bugfix release:

• fixed failed detection of tools for 32 bit system
• fix core uninstall on Windows
• do not exit-error if a library with invalid (non-semver) version is found
• do not crash if invalid FQBN is used in compile
• changed ARDUINO define constant to 10607 (improve compatibility with arc32 core)
• core list now do not crash with manually installed cores