replace levelDb with SQLite for Vault
consistent db_path (always file_name)
connect to database each time
removing leveldb
style correction
switch back to open database connection only once; call checkpoin after every certain amount of write operations(Put or Delete)
Merge branch 'next' into MAID-10_replace_leveldb_with_sqlite
Update maid_account.md
Update maid_account.md
Update maid_account.md
Update data_manager_account.md
Update data_manager_account.md
Update account_transfer.md
Update mpid_messaging.md
Merge pull request #22 from maqi/MAID-10_replace_leveldb_with_sqlite

Maid 10 replace leveldb with sqlite
Update and rename pmid_mpid_create_store.md to pmid_create_store.md
Merge branch 'next' into MAID-278_fix
Style fix.