- removed the old test_remove_environment
- modified the create_fake_environment to current specs
- add tests for removing package_sets and releases

Add tests that check our argument parsing logic (and fix bug)

See merge request !113

- going the arguments provided by the user
- to the relevant function being called.

Added tests because I discovered a bug that the tests would have caught.

Add example for `get_available_releases`

See merge request !111

return available (i.e. released!) release versions

See merge request !110

from available package sets

More code, but less thinking to understand what it does.

i.e. if mpsd_release == None

It's not perfect that this needs manual updating. On the other hand, this
provides control over what versions are (trivially) visible to users.

Use mpsd microarch consistently

Closes #33

See merge request !108

Remove conditional dependence on rich

See merge request !106