First take at #2, GitHub style tables

Supports thead, tbody, align and inline.

Example:

```
| *Head 1* | Head 2 | Head 3 |
|: --- |: --- :| --- :|
| Left | Center | `Right` |
```

Notes:

* pipes need to have a space on either side, except when aligning
* leading/Trailing `|` optional
* whitespace gets nommed
* inline pipes will probably not work, use `&#124;` instead?