Make hidden cells persistent over save/load.
Change icon. Move registration of button to init_hide_input.
Typo in comments
sync master
Add hierarchical_collapse notebook extension
fix typos
Add use strict and fix sloppy code. Enable work-around for non-triggering notebook_load.Notebook event.
call init instead of registering an event.
Remove comments about initialization.
Fix toggle bug and enable toggling when non-heading cell is selected.
Add comments.
remove spaces at end of line.
Merge pull request #16 from bjanssen/master

Add hierarchical_collapse notebook extension