Added sharding of secondary indexes tables
Polished secondary indexes API for a bit

Fixed method names:
* update_indexes -> set_indexes
* check_indexes -> list_indexes

Changed find_indexes_result_entry::indexes to std::vector<index_entry>
Removed deprecated code for find_indexes method
Added magic data before index table
Added storing of shard_id/count in index table
Merge pull request #167 from euroelessar/master

New shared secondary indexes