Install documentation for vala
I'm using vapis from https://github.com/apmasell/vapis from a recommendation of @ricotz, using "has_typedef=false" is missing. I went through background on this and found https://bugzilla.gnome.org/show_bug.cgi?id=794920.
@astavale I think that makes https://wiki.gnome.org/Projects/Vala/LegacyBindings#Delegates little obsolete, should we udpate that part? I have rights to do it, but I'm not confident enough to do myself.
Wonder if move documentation to project (maybe using sphinx http://www.sphinx-doc.org/en/master/) could help to keep that easily in sink and allow people to locate info about vala easily if they install it locally.