tag-generic-attribute-script doesn't allow underscores

[boughtonp]

Atom highlighting breaks when there's an underscore in an attribute, even though CF allows this.

The fix is probably changing the match regex from \\b([a-zA-Z0-9:-]+)\\b to \\b([a-zA-Z0-9_:-]+)\\b (or just \\b([\w:-]+)\\b).

However, that permits numbers colons and hyphen at the start of an attribute, which are all disallowed, so it should be \\b([a-zA-Z_][a-zA-Z0-9_:-]*)\\b (or \\b([a-zA-Z_][\w:-]*)\\b).

[David-Polehonski]

Could you add a test case for this, or attach an example snippet?