refs #219 - Updated docs for rapidsms.contrib.echo
refs #219 - Added tests for rapidsms.contrib.echo
refs #219 - Clarification that PingHandler requires precise text
Merge branch 'master' of github.com:rapidsms/rapidsms into docs/contrib/echo
refs #219 - Updated release notes
Merge pull request #249 from caktus/docs/contrib/echo

refs #219 - Tests and docs for rapidsms.contrib.echo