Switched to JSHint for Node.js diagnostics

This pull request switches from using JSC with the custom python script to Node.js with the JSHint command-line tool.

This allows users to override the JSHint options in the following order:

* `/* jshint */` comments
* `$CHOC_PROJECT_DIR/.jshintrc`
* `$HOME/.jshintrc`

Users can also configure JSHint to skip some files by listing them in a file named `.jshintignore` in either of the directories above as well.