Merge branch 'master' of https://github.com/cbhaley/calibre
Update Harvard Business Review
Caravan Magazine by Kovid Goyal
ODT Input: Only use the first image as cover

ODT Input: Only treat the first image as a cover if it is of suitable
size, instead of any image in the document. See #1224157 (ODT to MOBI - Images - Cover Image will not removed and other images are missed)
pep8
version 1.3
Recognize EMF images
DOCX Input: Do not fail if the firs image is an EMF image

Fixes #1224849 [DOCX to EPUB conversion failed with devide by zero](https://bugs.launchpad.net/calibre/+bug/1224849)
Remove unused code
Il Cambiamento by ghib9
In the comments editor, permit insertion of references to images on the 'net (<img ...>) as well as links (<a ...>).