v0.6.1

This release fixes two faults of the driver databend of v0.6.0, which usql found and measured. No other driver changes.

What changes for a caller

• Databend. A connection keeps its session for as long as it lives, so USE and SET stay in effect when database/sql hands the connection to the next statement, as a pooled connection of MySQL does. In v0.6.0, the driver reset the session each time the connection went back to the pool, so a caller that runs each statement through *sql.DB, as usql does, lost a USE at once. The driver no longer implements driver.SessionResetter (D126). A caller who wants the session of the DSN again opens a new connection.
• Databend. After a transaction fails on the server, Commit and Rollback now send the ROLLBACK that ends it. In v0.6.0, the driver refused its own ROLLBACK, and the server kept the transaction aborted until the connection closed.

Other changes

• TDengine gets no driver here. Its REST interface ends a result that failed as valid JSON with code 0, so a driver cannot tell a cut result from a whole one (D127). docs/TDENGINE.md holds the measurements. Apache Pinot is the next target.