Add 'move' keyword to emacs, kate, and vim editor modes.
auto merge of #18793 : swgillespie/rust/master, r=alexcrichton

I noticed today that `move` wasn't getting highlighted in my editor of choice (emacs), so I went ahead and added it as a keyword in the emacs, vim, and kate editor files. Apparently it has already been done for gedit.
Document ast::Ty_
Try to remove ty_nil, some kind of error in exhaustiveness checking
Complete the removal of ty_nil, ast::LitNil, ast::TyBot and ast::TyUniq

[breaking-change]

This will break any uses of macros that assumed () being a valid literal.
Update tests accordingly
Update the reference