Walverine integration

Not quite ready for prime time.

Remaining issues:

- `match` isn't ideal. A quick solution is just explaining such in the README.
- `Citation.find(text, {type: "judicial"})` throws: 

```
TypeError: Cannot read property 'type' of undefined
    at /Users/adelevie/programming/citation/citation.js:113:34
    at /Users/adelevie/programming/citation/node_modules/xregexp/xregexp-all.js:1016:36
    at String.replace (native)
    at String.fixed.replace (/Users/adelevie/programming/citation/node_modules/xregexp/xregexp-all.js:999:36)
    at Function.self.replace (/Users/adelevie/programming/citation/node_modules/xregexp/xregexp-all.js:731:32)
    at Object.Citation.find (/Users/adelevie/programming/citation/citation.js:108:30)
    at Object.exports.(anonymous function) (/Users/adelevie/programming/citation/test/judicial.js:44:27)
    at Object.<anonymous> (/Users/adelevie/programming/citation/node_modules/nodeunit/lib/core.js:235:16)
    at /Users/adelevie/programming/citation/node_modules/nodeunit/lib/core.js:235:16
    at Object.exports.runTest (/Users/adelevie/programming/citation/node_modules/nodeunit/lib/core.js:69:9)
```

- Internal API inconsistency. For now, Walverine is like the ugly step child. But hey, it works!
- Docs, in general, should probably give a more thorough explanation of the various types, and how `judicial` works differently.