The single-group-by queries SQL for TimescaleDB was missing a comma
after the time grouping, creating an incorrect SQL statement. In
addition, a sanity check is added to make sure there are other
select clauses besides just the time grouping.

This also includes minor nits including:
 - fixing the alphabetical order in the README
 - have the generate_queries script output a symlink per query
 - add support for the -timescaledb-use-time-bucket flag to scripts