Merge pull request #584 from chrox/master

remove full screen option in koptoption
Added a pure Lua gettext implementation
don't accept empty strings as valid translations
don't build .mo files, we read .po now
Merge pull request #586 from hwhw/l10n

Added a pure Lua gettext implementation.
Tested and working.

The translations are rather lacking, though!
Update language.lua

The list of languages is updated. So now all the translations at least partially present in Transifex are selectable.
add android build target
use mupdf to handle zipped image files
initial commit for android port of koreader
This PR just shows how far we have went to
the android port. There is still a few steps before a running
android port.