Adding node globals to grammar

This addresses issue #45 by adding 2 new grammar rules:

 * `require` = `support.function.js`
 * `module`, `exports`, `__filename`, `__dirname`, `global`, `process` = `support.variable.js`

I'm willing to drop `global` and `process`, since that wasn't mentioned explicitly in the ticket. Of course I'll make any other changes requested to merge this in.