Use _ when merging labels. Allow more than one interpretation per node in the interpretations layer
PEP8
Look forward further when disambiguating markers.
When determining a headers parent, only skip over p# and h#s; everything else has a correct position
Document regex better
Merge pull request #166 from cmc333333/appendix-depth-forward

Look forward further when disambiguating markers
Merge pull request #165 from cmc333333/multiple-interps

Allow multiple interpretations for the same node
Remove stray print statement in the test
Merge pull request #167 from cmc333333/appendix-depth-backwards

Tighten positioning of headers with unclear depth