Feature, implement :main command

Hi, Attached is a patch that adds a :main command to hugs. :main arguments is equivalent to arguments `withArgs` main, but easier to use because you don't need to import anything extra, and the arguments are parsed as if they were arguments - i.e. :main my test "of this", instead of ["my","test","of this"] `withArgs` main. Since i don't know a whole lot about this area of the compiler, and it is changing the user interface for everyone, I thought it best that someone checks its at least sane before i do anything with it. Thanks Neil