Supporting highlighting of many syntactic elements

[giordano]

With #17 we now have syntax highlighting for

1. &-lines
2. @-lines
3. protocol lines (#)
4. comments (also # but different from protocols)
5. $-lines
6. linkage lines (||, >>, and <<)
7. text lines (starting with .*\.)
8. additionally, we may want to highlight differently special keywords in $-lines (see Syntax highlighting for ATF #1 (comment))

Texmate grammar has plenty of different default syntactic groups/subgroups and we're using a few of them, the problem is that colouring is delegated to themes, over which we have no control. Apparently not even the default themes have a comprehensive coverage of standard Textmate grammar elements, so depending on the theme, some items may not be highlighted, or different elements may have the same colour. Note that apart from comments, all other items can (ab)use most standard syntactic items, ATF isn't really a regular programming language.

One option is to maintain ourselves themes (light and dark?) which cover all syntactic elements we care about