Minor rewrite
Minor rewrite

A few changes before merging into main branch:
- Create UnsupportedDevice exception class, to simplify catching exception
  in user code.
- Create read-only properties for available_services and
  service_version.
- Check that service version is supported once (in __init__), to avoid
  code duplication.
- Renamed a few variables for PEP 8 compliance.
- Bumped version

(cherry picked from commit 43d9f41ac8de990dd3e27dcbc5d000e25c9df875)

stianaske/pybotvac