Squashed 'mupdf/' content from commit b2f096d

git-subtree-dir: mupdf
git-subtree-split: b2f096de23e5341fbbcd7c290f3a144423741906
Merge commit '63812b7a7f52f349018993b9b4c48b21ed1aebf9' as 'mupdf'
Use a fork of the openjpeg repo modified for Nspire and add .gitmodules to root of repo