New features:
- add support for hypothetical indexes on expression
- add a hypopg_get_indexdef() function to get definition of a stored
hypothetical index
Bug fixes:
- don't allow hypothetical unique or multi-column index if the AM doesn't
support it - disallow hypothetical indexes on system columns (except OID)
- fix indexes using DESC clause and default NULLS ordering, thanks to
Andrew Kane for the report and test case. - fix PostgreSQL 9.6+ support, thanks to Rob Stolarz for the report
Miscellaneous:
- add support for PostgreSQL 10