Leksah ported to haskell-gi

[Hamish Mackenzie]

We have ported Leksah from Gtk2Hs to haskell-gi. There should be
no noticeable difference in the UI, but going forward we will
have less to do to add support for new Gtk+ features (Gtk2Hs
was manually updated on a as needed basis, but haskell-gi
automatically generates bindings).

So far the code is only in GitHub, but if you want to try it out
you can use Xobl Leksah or follow the instructions here:

https://git.io/vVF2x

Thanks to everyone that helped out! Especially to Iñaki and
Jonas, haskell-gi is lovely!!!

Hamish