fix for #9:
- added documentation version as variable in mkdocs.yml (extra.documentation_version)
WARNING! Gitlab maintenance operation scheduled for Thursday, 18 June between 19:00 and 20:00 (CET). During this time window, short service interruptions (less than 5 minutes) may occur. Thank you in advance for your understanding.
- added documentation version as variable in mkdocs.yml (extra.documentation_version)