Remove minor redundancies in macros importing

Fix sys.executable usage

Use the same Python for tests as the test runner was invoked with.

Use `importlib` instead of the deprecated `imp`.

Contribution info in README

Remove obsolete travis build file

Add build status badge to README

Add sourcehut builds file

Also: do not create poole shortcut shell file as pooly.py is very likely
used in per-project virtual envs which have dependencies according to
the macros.py file used in a project.

Use sourcehut wiki for docs beyond README

BitBucket wiki pages are now in the in-repo docs folder