Changed the execute function to handle an objx.Map of args

It seemed like some commands would benefit from allowing extra arguments, especially the new 'watch' command that I'm putting together.  Instead of having 'gorc watch test', 'gorc watch vet', and so on, each being a separate commander target, I would rather allow for 'test' and 'vet' and such to be options that can be passed to execute(WatchCommand).  It would be especially useful if you wanted multiple types of output, e.g. 'gorc watch coverage vet' to output coverage test results followed by vet results each time files are changed.