Test suite

Alright, I've got the test suite for highlightjs. The only thing on the list that I didn't implement yet is:

> compare produced markup against control samples with all supported language features

This one is going to be pretty big and I will need help on it. I'll most likely merge this in before we get into completing the final step as #531 is reliant on this being merged.

**Edit**: To actually run this you need to build the node version of the project.

So right after pulling this branch down:

```bash
python3 tools/build.py -t node
npm install
npm test
```