Allow numbers and underscores in attribute selectors

[dmcass]

This PR incorporates the fix from PR #876 and adds the fix for #863, and also adds a test case that covers both.

[Synchro]

Though this does fix the bug as reported, I agree with other comments in #876 that we should accept anything that's valid, which is quite a bit broader than this regex. Can save that for another day though.

[dmcass]

Added a commit to make character classes in regular expressions consistent across the parser.js file. I'll work on extending allowable characters when I have time, but that's a much bigger job considering that you have to account for escapable characters, most UTF8 characters, etc. I'm not sure it's within the scope of this pull request.

[dmcass]

So I put a little time into extending support to all valid attribute selectors, and it makes me question how necessary it really is because its complexity is absurd. The really crazy part is that this doesn't even support the full character set (can't use unicode characters higher than \uffff in JS).

The regex which will match all valid attribute selectors (any valid ident token from the CSS syntax rules):
/^-?(?:[_A-Za-z\u0080-\uD7FF\uE000-\uFFFD]|\\[A-Fa-f0-9]{1,6}|\\[\u0020-\u007E\u0080-\uD7FF\uE000-\uFFFD])(?:[_A-Za-z\u0080-\uD7FF\uE000-\uFFFD-]|\\[A-Fa-f0-9]{1,6}|\\[\u0020-\u007E\u0080-\uD7FF\uE000-\uFFFD])*/

So, the question is, does the parser need to be 100% complete in its support of CSS, or only support the majority of use cases? @agatronic, @MatthewDL, @cloudhead, or anyone else who is actively maintaining: can I get your input here?

[Synchro]

Par for the course for anything from the W3C! I agree that it's outside the scope for this issue, which is what I meant about being able to wait. While it's in the spirit of 'be liberal in what you accept and strict in what you emit', in practice it's unlikely to be needed any time soon, and the regex you wrote will come in handy if it does get revisited. Thanks for cleaning up all the regexes.

[zackd]

would desperately love a new release with these fixes! :)

thanks for the awesome lib!