Bulk insert records in batches of 1000 per INSERT statement

- yields vast speed improvements especially when a table has multiple indexes
Refactor and fix using alternate serialization helper classes
Add JSON serializer classes
Merge branch 'bulk-insert'
Merge branch 'json-db'
Add json_db files to gemspec; adjust gem description
Adjust README for added JSON serialization
Bump version to 0.3.0