Remove allowBackup property from manifest
Remove uses-sdk attribute (overriden from build.gradle)

Signed-off-by: Daniele Ricci <daniele.athome@gmail.com>
Depend on Android support library 20.0.0

Signed-off-by: Daniele Ricci <daniele.athome@gmail.com>

Conflicts:
	library/build.gradle
Merge conflict with previous commits
Merge pull request #33 from necronet/master

Remove allowBackup property from manifest
Merge pull request #37 from daniele-athome/master

Build against API level 21/build tools 21.0.1