Handle inline graphics correctly

[Delivers #62972972]
Use \includegraphics for inline images

[Delivers #62972972]
Omit colon in captions with only a label

[Delivers #62973876]
Add some failing tests

[#62973860]
Override convert_standalone_image

[Delivers #62973860 #62973874]
Issue pull request for branch centered-image-no-caption-62973860

[Delivers #62973860](https://www.pivotaltracker.com/story/show/62973860)
[Delivers #62973874](https://www.pivotaltracker.com/story/show/62973874)
[Delivers #62973876](https://www.pivotaltracker.com/story/show/62973876)
[Delivers #62972972](https://www.pivotaltracker.com/story/show/62972972)
Speed up label detection using a global salt

[#62973860]
[#62973860]

* centered-image-no-caption-62973860:
  Speed up label detection using a global salt
  Issue pull request for branch centered-image-no-caption-62973860
  Override convert_standalone_image
  Add some failing tests
  Omit colon in captions with only a label
  Use \includegraphics for inline images
  Handle inline graphics correctly