Bug Fix
* Fixing deallocating None bug 201
* Clickhouse support on new version 165
* Shrink array before return for arrow2 to reduce memory usage when result is small 196
* Fix Oracle port error 209
Others
* Improve Oracle performance by enlarging array size using prepared statement 127
* Upgrade arrow2 to 0.9 221
* Add Postgres Json, TimestampTz support to arrow2 235 229
* Clean up python dependencies (remove ones for benchmarking)