Feature add doccomments

[pbeart]

Outstanding:

• Doc-comment not targeting anything should be a warning

[VonTum]

Hmm, any doc_comment is also a valid match for single_line_comment. Best to make them explicitly disjoint (by adding ^\/ to single_line_comment

[pbeart]

Seems as though tree-sitter supports a not-quite "normal Regex" level of regular expression parsing (apparently LR(1)), so e.g. start-of-line characters don't seem to be allowed. Given this, it seems like making the regexes disjoint may not be possible and therefore it might be better to use tree-sitter's well-defined conflict resolution features e.g. precedence to make sure there are no improperly interpreted cases.