#859 Support cwl magic comments

[Anonymous]

I would like to be able to write something like the following in any tex document

%!TeX CWL = \foo{num}#m

and have txs add \foo{num} to the auto-complete list when in maths-mode.

In general I would like to be able to use magic comments to define custom completion word lists (cwl) for any tex document (whether it be a main tex document or an included text document).