Add ability to create elastic search JSON closes #28

Summary:
Using harvests2json and a compressed mws index, one can generate JSON files
for elasticsearch.

Some bugfixes.

Addressed comments

Test Plan:
./bin/mws-index -I ./data/zbl/ -o Index/
./bin/harvests2json -I Index/ -H ./data/zbl

Reviewers: cprodescu

Reviewed By: cprodescu

Differential Revision: http://phab.code4fun.de/D68