Merge pull request #718 from patternleaf/715-modal-viewer-toc

715 modal viewer toc
Update changelog

Addresses #715
Avoid race condition when updating index

Signal handlers are used to update the search index when SectionAsset
instances are deleted.  This works fine when they are deleted
explicitly, but causes a problem when they are deleted via the cascade
when the related Section is deleted.  When the section is deleted, the
story can't be fetched via ``instance.section.story``.  To work around
this, story a reference to the story in a ``pre_delete`` signal handler
so its available in the ``post_delete`` signal handler.

Addresses #723
Merge fixes for #723 into develop

Conflicts:
	README.rst