maker.py: Adds autofill support for select mirrors

github.com, git.overlays.gentoo.org, and bitbucket.org
mirrors will have their extra source URLs, homepage, and
feeds filled out for them automatically.
maker.py: Adds Exception raising for errors
maker.py: Migrates prints to self.output messages

Also cleans up large messages to tidy up the code and make it more
legible.
utils.py: Adds get_input() and get_ans() functions

maker.py: Migrates to get_ans & get_input from utils.py