Adds disk cache as a backend and some cleanup
What's Changed
* remove the unused max and min feature size from the DBs by icfly2 in https://github.com/banking-circle-advanced-analytics/simstring-fast/pull/38
* Add diskcache by icfly2 in https://github.com/banking-circle-advanced-analytics/simstring-fast/pull/36
**Full Changelog**: https://github.com/banking-circle-advanced-analytics/simstring-fast/compare/0.2.5...0.2.7