Replace them with:
* containers' hostnames
* gateway's IP address for default SMTP_HOST
* Core: when SMTP_HOST undef, echo the default value
* docker-compose: add port mapping
* docker-compose: drop network driver conf
* Exim macro: use localhost as LMTP host
* Update README.md
* docker-compose: Limit port mapping to loopback
* Update other docker-compose example files
This way we can depend on alpine's python3 package which is binary
compatible with the rest of the python packages in the distribution.
This requires spelling out python3 explicitly in several places since
alpine still defaults to python 2 for /usr/bin/python.
* Use old style middleware settings for Python 2.
* Make entrypoint python2 and 3 compatible.
* Fix python command to test for mysql server.
* Bettery docker-entrypoint to work with Python 2 & 3
* Add missing braces.
* Update mailman-web to use Python 3
* Update configuration
* Python 3.6 image.
* Use alpine 3.7
* Use new style middleware
* Use alpine 3.6
* In Python 3, urlparse was renamed to urllib.parse
