Disable footer and relbar for epub

Signed-off-by: Michal Čihař <michal@cihar.com>
Add basic epub cover image

Signed-off-by: Michal Čihař <michal@cihar.com>
Simplify code

Signed-off-by: Michal Čihař <michal@cihar.com>
Merge branch 'master' into bootstrap