Implement derivatives hook.
Add function comment and get rid of unused variable.
Merge pull request #95 from adam-vessey/7.x-derivatives

Implement derivatives hook.
Merge branch '7.x' of github.com:Islandora/islandora_solution_pack_book into 7.x
added form alter
added additional mimetypes
take care of this outstanding issue via @nigelgbanks comment from https://groups.google.com/forum/#20bookobjects/islandora/8Ptf6ZVHkA4/JlS16B6SMMsJ
Merge pull request #98 from ruebot/7.x

take care of this outstanding issue via @nigelgbanks comment from https:...
added ability to ingest jpeg pages
Merge branch '7.x' of github.com:Islandora/islandora_solution_pack_book into 7.x
made derivatives state aware