Port PR merge script from Spark
Port PR merge script from Spark

This ports the PR merge script from Spark, similar to what https://github.com/databricks/spark-avro/pull/81 did for spark-avro.

falaki, let's use this script from now on when merging PRs in order to keep the commit history clean.

Author: Josh Rosen <joshrosen@databricks.com>

Closes #146 from JoshRosen/merge-script.

sunilyadavsky/spark-csv,abridgett/spark-csv,databricks/spark-csv,gasparms/spark-csv,YanjieGao/spark-csv,YanjieGao/spark-csv,gilv/spark-csv,YanjieGao/spark-csv,gilv/spark-csv,abridgett/spark-csv,falaki/spark-csv,abridgett/spark-csv,falaki/spark-csv,sunilyadavsky/spark-csv,databricks/spark-csv,falaki/spark-csv,sunilyadavsky/spark-csv,gasparms/spark-csv,gilv/spark-csv,databricks/spark-csv,gasparms/spark-csv