fix(rows): doesn't close rows on Scan (#49)

feat(string): added nullable String/Null for sql/json (#47)

!feat(dtc):renamed Context and added DTC (#45)

fix(tx): added context in tx.QueryBuilder and tx.QueryRowBuilder (#42)

* fix(tx): added context in tx.QueryBuilder and tx.QueryRowBuilder

* chore(docs): updated CHANGELOG.md

fix(db): fixed StmtMaxIdleTime and time.After issues (#38)

fix(query): added LimitResult/LimitOption/NewOrderBy/WithOrderBy (#36)

fix(orderby): improved OrderByBuilder for api input (#34)

feat(sqlbuilder): added OrderBy (#32)

fix(db): Multi-DHTs support and stmt reuse bug (#31)

feat(shardid): added DHT for sharding (#30)