Timml

* Some minor documentation updates by dbrakenhoff in https://github.com/mbakker7/timml/pull/109

Minor bug fixes and additions, including:

Fixed bug in legend of contours from mpl > 3.5. Should be changed again in future when mpl gets fixed.
Return contour sets when calling contour

**Full Changelog**: https://github.com/mbakker7/timml/compare/v6.3.0...v6.4.0

Extension of BuildingPit element.
Some work on the docs.

**Full Changelog**: https://github.com/mbakker7/timml/compare/v6.1.2...v6.2.0