Building Heptapod forked Golang components
Heptapod Workhorse and Shell require to be built from a repository rather than just a tarball (same as their Git upstreams). This is also the simplest for the release process.
These changes swap the upstream Git repos for the Mercurial repositories, building versions specified in HEPTAPOD_*_VERSION
files, hence in the spirit of heptapod#352 (closed).
Closes #5 (closed)