This is a big diff that implements the following changes:

* Move the individual icon types to sub-pages so this information isn't so overwhelming on a single page
* Create new margins graphics for each type of icon that are more clear and contextually-appropriate
* Be clearer about which sizes are used for each icon type and style
* Add real captions to images by using the `.. figure::` tag
* Replace some images with better ones
* Improve wording in some places