GitHub repository for Haskell-related ports

[Gleb Popov]

We've got a repository under freebsd organization on GitHub [1]! Let's
thank bapt@ for that.

I will happily accept pull requests there, if FreeBSD Bugzilla or
Phabricator instance do not suit you.

Right now there is ghc-upgrade-883 branch, which contains work-in-progress
update of lang/ghc and all haskell-related ports. Any help in this branch
is also welcome.

[1]: https://github.com/freebsd/freebsd-ports-haskell