If SQLite3 apt install fails, still write python-sqlite3-version so
steps/python doesn't clear the python cache and re-download the runtime
on every build. Avoids repeated full re-downloads + builds.

apt-get update fails because apt.postgresql.org dropped the xenial-pgdg
repo (404), which under set -e silently killed every build. Skip SQLite3
gracefully instead; python runtimes ship the sqlite3 module already and
apps on this stack use postgres.

Python 3.7.3 release

* new runtimes

* update default latest

* new recipe for new runtime

* add new runtime formula

* add test updates for new runtime release

* wrangle tests into submission

* update tests to use default_pythons

* delete commented code

* new recipe for new runtime

* add new runtime formula

* wrangle tests into submission

* track usage of older feature steps

* remove typo whitespace

* make buildvars consistently cased

V 147

Update readme

update changelog

Document tests

Test updates