Merge branch 'master' into develop
Change all required level names to try/except with fallback to level numbers

Problem: If someone want to quickly add an io system, setting the required
level names for the multiindex is a huge overhead.

Solution: If level names are available, use them. Otherwise reley on the level
numbers
added change to changelog
started with wiod parser - wip
First test cases for mathematical functions
Fixed the get_extension doc
full math test, full run test
fixed documentation
updated notebooks and changelog, rebuild docs
Merge branch 'develop'