Add commandArgs parser to Y.K.V.Ex.Common.

Useful for Cabal/Make/Shell ex commands. Generic shell-style args parser
that is a bit smarter than the current one (ie, it can handle quotes
without dying)
Update Cabal & Make Ex Commands to use commandArgs.

:cabal and :make are now slightly smarter.
Add :! Ex command. (Generic shell call)

Uses the "build" primitives same as cabal, since they aren't actually
very build-specific.