Provide Jaccard and Haversine comparators and move comparator modules to own directory

Per Forest's request, this duplicates pull request #91 and does the following:

- Provides Jaccard and Haversine distance measures
- Provides tests for both
- Updates setup.py to put the distance modules (affine, jaccard, haversine) into a `distance` directory and imports the submodule as `dedupe.distance`.

%timeit reports 3.9us per iteration for the compareLatLong routine; and 2.7us for the Jaccard routine.