Argument migration

Add a DSL to migrate options to different names, migrate them from either being manually passed or from tabs and print a warning telling users to use the new name. Also, migrate `wget` as an example.

CC @adamv @mistydemeo @jacknagel @tdsmith @asparagui for thoughts and review.
Can we wrap this in an `if @flags.include?(old_flag) ... end`? I found the `next unless` in the middle of the block a little confusing at first.