WIP: Try rubocop

Rubocop was discussed a bit a while back.  I thought I'd give it a shot.  This is a WIP trying to figure out what checks to enable/disable and whether or not we want to use it.

Feedback wanted.
I'm definitely not a fan of adding an extra `begin`/`end`. I'm also not a fan of dropping the leading `if` down a line, it just is difficult for me to read. In general I tend to use either the aligned hanging indent or the previous style.