cleaner toctree collapsing
remove unused images
Fixes to HMM docstrings
Clarification of the sequence length, per @ogrisel
Merge pull request #2525 from rmcgibbo/hmmfix2

Fixes to HMM docstrings
Merge pull request #2517 from jaquesgrobler/simpler-collapsible-toctrees

Cleaner Toctree collapse for useguide