Support constants

[alxtz]

In the official language-javascript package, variables declared with const or in all caps would mark the syntax--constant class Much syntax themes support this syntax--constant class, I think it would be awesome to have this added ( or give some advice about how I can contribute to this )

[gandm]

In the first example language-babel does this

In the second case the problem lies with having multiple coma separated vars. language-javascript breaks like this. This issue has been raised before. See here