Word Autocompletion

[Clashsoft]

Add autocompletion (Ctrl-Space) for the following things:

• attributes, templates and functions: given foo(bar) ::= << ... >>, < Ctrl-Space → foo(), bar, first(), length(), etc.
• options: <foo; for Ctrl-Space → format; <foo; Ctrl-Space → separator, format, null, etc. Maybe it could also insert the trailing =
• other reserved words in their respective contexts