Add Missing Docstring for Functions

[tomschr]

These functions don't have a docstring:

• input_format_check in docmanager/__init__.py
• logmgr_flog in documentation/logmanager.py
• init_default_props in documentation/xmlhandler.py
• the whole Handler class and its methods in docmanager/xmlutil.py

[mschnitzer]

I've documented my functions in https://github.com/openSUSE/docmanager/commit/282749d7eb28127ba01bb203a743aa0114addfe0

Can you please document your functions? Thanks!

[mschnitzer]

Can be closed now. Thanks Thomas for providing your documentation!