fixed clear() concept of internal values (pre_clear(), post_clear())
segmented meshes with only 1 segment are now written as vtu
points functionality is now based on mesh and not on segment to support segments without vertices
Added unchecked_add function for adding elements to segments which does not check if element is already in the segment
Added thin config meta functions
added cell only segmentation meta function, added doxygen documentation
added for_each_boundary_element with typelist
added thin configs and cell_only configs
tag names start with a small letter now
bug fix: parameter ordering
using field instead of accessor
bug fix: tempalte type construction in thin segmentation
added new example: thin mesh