Take authors on command-line.

When doing things programatically, it's annoying to have to do input on a
prompt; even when doing things interactively, it still is. :)

This allows us to enter some number of authors after the license name;
if it's zero, we'll still prompt like before.

Since the author is part of every single license, pull out the prompting
one level to licgen itself, rather than erb.
Fix spec.

Authors is now required either via arg or gets input.
Update the README with better template info.
Update cucumber features with authors scenarios.
Merge branch 'take-authors-on-command-line'
Bump version to 0.4.0