Update README.md

doc: add Android Arsenal badge.

refactor: update gradle to 2.1.0

chore: update readme

fix: update gradle plugin

docs: readme

fix: setRational to setRationale

fix: ensure we unregister the activity comparing by name

refactor: change request() method by requestPermissionForResult() in the case where annotated methods are used

docs: update lib gradle dependency version

docs: update lib gradle dependency version

docs: README

docs: tidy up README

chore: version code 4 (0.3.0)

docs: add some documentation about priming and rationale messages