Minor tweaks to template tags and man. commands
Document template tags

Man, that was dull...
Remove unused template tag (image_tags)
Be consistent in how template tags are registered

Using the same function name as the tag name paves the way for using
autodoc for the reference section...
Move templatetag docs into docstrings and use autodoc
Split filters and tags into sections
Rename reviews_tags to reviews_filters

As it only contains filters