v3.6.0

Features

• add RPC priority support (#324) (51533b8)
• add support for low-cost instances (#313) (44aa7cc)
• spanner: add processing_units to Instance resource (#364) (113505c)
• update query stats samples (#373) (c1ee8c2)

Bug Fixes

• db_api: use sqlparse to split DDL statements (#372) (ed9e124)
• db_api: classify batched DDL statements (#360) (b8b24e1)
• deps: add packaging requirement (#368) (89c126c)

Documentation

• omit mention of Python 2.7 in 'CONTRIBUTING.rst' (#1127) (#374) (b7b3c38), closes #1126