This patch removes code support for PG9.6 and PG10. In addition to
removing PG96 and PG10 macros the following changes are done:
remove HAVE_INT64_TIMESTAMP since this is always true on PG10+
remove PG_VERSION_SUPPORTS_MULTINODE
Release Docker builds are now provided in a separate repository,
https://github.com/timescale/timescaledb-docker.
Tests and development builds for Docker are now provided
by two new scripts in the scripts directory:
- `docker-build.sh` to build a development image from current sources.
- `docker-run-tests.sh` to run tests for current sources through a Docker container.