Make completion menu avoid right of screen as well as bottom.
Add a reStructuredText code model.
Add a UnionTokenizer, which combines multiple tokenizers.
Modify SyntaxHighlighter to work with UnionTokenizer.
Move syntaxlib into core.

--HG--
rename : stem/plugins/semantics/syntax.py => stem/core/syntaxlib/syntax.py
rename : stem/plugins/semantics/syntaxlib.py => stem/core/syntaxlib/syntaxlib.py
Update proxy icon on first save of a new file.