Adding linting via JSHint

This pull request is the beginning of some work which adds linting to underscore-contrib via JSHint. For the moment I have two questions for @fogus:

1. Is linting something you are interested in having? I think with the appropriate settings it could be useful in enforcing the sort of coding style you'd like to see in the project.
2. If you are, will you be able to give some feedback as I set this up? I'll probably need to ask several questions about preferred coding style to determine whether to change existing code or adjust the JSHint settings.

Assuming you're open to that, I'll use this pull request to ask style questions as I come across them.