Merge branch 'xlog-decoding-rebasing-remapping' into HEAD

Merge branch 'xlog-decoding-rebasing-remapping' into HEAD

* xlog-decoding-rebasing-remapping:
  wal_decoding: Temporarily add logical decoding regression tests to everything
  wal_decoding: design document v2.4 and snapshot building design doc v0.5
  wal_decoding: test_logical_decoding: Add extension for easier testing of logical decoding
  wal_decoding: pg_recvlogical: Introduce pg_receivexlog equivalent for logical changes
  wal_decoding: test_decoding: Add a simple decoding module in contrib
  wal_decoding: logical changeset extraction walsender interface
  wal_decoding: Allow walsender's to connect to a specific database
  wal_decoding: Only peg the xmin horizon for catalog tables during logical decoding
  wal_decoding: Introduce wal decoding via catalog timetravel
  wal_decoding: Add option to use user defined tables as catalog tables
  wal_decoding: Log xl_running_xact's at a higher frequency than checkpoints are done
  wal_decoding: Add wal_level = logical and log data required for logical decoding