processor: add tests.

@duncanbeevers , I wonder what do you think about stack processor rewrite and tests. Do you know about more stack examples that are worth to be tested?

For such tests, it might be nice to simply have pairs of fixture files, one containing a stacktrace string and the other containing a JSON representation of the expected parsing.

`firefox14-29.raw.json`
```json
"firefox-stack-..."
```

`firefox14-29.parsed.json`
```json
[{"function":"line 7 > eval line 1 > eval", ... }]
```

This makes it a lot simpler to add new tests in the future without a lot of boilerplate.