Better error message when failing to find /usr/local/lib?

[agnoster]

See #199, when installing and there's no parent dir for MINT_PATH, the install fails with a somewhat inscrutable error message (it takes a little digging to figure out what's wrong).

It might be nice to have an error message if MINT_PATH doesn't exist and can't be created that gives the full path we expect to find, instead of just Error: You don’t have permission to save the file “0.42.0” in the folder “build”.

[yonaskolb]

Core issue fixed here #216