Node.js support!

Implements issue #54.

Good news: I was able to use the existing Jasmine tests and run them on Node too, via [jasmine-node](https://github.com/mhevery/jasmine-node). (Skipping the jQuery tests, of course.)

```
$ npm test

> mailcheck@1.0.3 test /Users/aseemk/Projects/Node/mailcheck
> jasmine-node spec/

.............

Finished in 0.025 seconds
13 tests, 50 assertions, 0 failures, 0 skipped
```

Hope you like. =)

(Don't forget to publish to npm if you do. I didn't think I should be the one to do that.)