Cabal-add: extend Cabal build-depends from the command line

As discussed at Convenience in the Haskell ecosystem - #169, I’ve developed a small command-line tool to add build-depends. I tried a few examples and convinced myself that it’s robust enough, but would appreciate more user acceptance testing before I decide to clutter Hackage with one more package.

$ cabal-add --help Usage: cabal-add (-f|--cabal-file FILE) [-c|--component ARG] DEP

  Extend build-depends from the command line 

Available options: 
  -f,--cabal-file FILE Cabal f...