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.
If we require a hash with exactly one key-value pair, should we just have two required arguments instead? Then ruby does the argument checking for us, and we don't need some of the hash manipulation below.