[ActionScript] refactor syntax

[jrappen]

• update to syntax v2
• add variables
• move comments to prototype context
• add named contexts for strings & comments while making use of meta_scope
• replace captures: 0: ... with scope: ...
• add more tests

[jrappen]

To anybody reviewing, you can check I haven't changed the regex for the variables by reversing my changes:

• remove whitespace
• replace (?:...) with the original (...)

[jrappen]

I'll address leftover comments later today.

[jrappen]

I still have to do the keywords context and update the numbers stuff.