Update outdated documentation and add documentation and references for the the new reverse binding support. Add a new example, reverse, that demonstrates how to use Android API directly from Go and thereby implement an Android app in pure Go. Change-Id: Iac054dbc015d00a37c0cc234931f9bd90172848e Reviewed-on: https://go-review.googlesource.com/31170 Reviewed-by: David Crawshaw <crawshaw@golang.org>