Buildpg

* avoid recursion in `funcs.comma_sep` and `select_fields` 36

* add `nulls first` and `nulls last` operators 23
* switch tests to github actions 32
* support asyncpg `v0.23` 32
* drop support for python 3.6 32
* uprev test dependencies 32

Fix usage of falsy values 18.

Add `ILIKE` operator