Issue #16

* Fixed: An issue, where PNG images exceeding the maximum specified
sizes were broken during resizing.
* Fixed: Issue #16, where ePub 3 multimedia needed to be added to the
automatic chapter processing.
* Fixed: Potential issue related to Issue #16 with loading large files
from external sources, where these might result in memory errors. These
will now be loaded into a temp file on the server, before being added to
the book.