Make Heptapod installable from source
For future deployments at Clever Cloud, we'll need to make Heptapod installable directly from its various sources.
In more concrete terms, that means getting rid of all things that have been hard-coded for the Docker context. Thanks to developments made for Heptapod 0.8.0rc1, this is not much more than making the global HGRC path and the hg
executable configurable.
I do have a working version running on a modified version of the GitLab Development Kit (GDK), it's reasonable to package it before 0.8.0, and it leads to simplification of its own.