v0.9-spark3.1

0.9 release for Spark 3.1. The features

• f5fd647 (Use the FutureDataInputStreamBuilder to open files).
• 2ec4122 (Configure readahead).

were omitted.

What's Changed

• Make Spark-3.1 branch consistent with main. by @pspoerri in #42
• Update Spark-3.1 branch to 0.9 by @pspoerri in #64

Full Changelog: v0.8-spark3.1...v0.9-spark3.1