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
PostgreSQL 12 is supported since 1.7, while 9.6 and 10 are deprecated.
This PR updates the building from source instruction with this change
and uses 1.7.0 in examples.
This commit updates the README with updated resources, including Timescale
Cloud, new support options, release notes, and others. For readability, it
also moves instructions for building from source to a separate readme file.