Use #public_send for attribute assignment

Closes #646
code example error in GETTING_STARTED.md fix

error due to incorrect use of instance variable fixed by use of closure
Allow selective linting

Closes #653
Update gems
Update rubygems source
Test against Rails 4.1
Reference released documentation

* GitHub displays docs from master which aren't released
* rubydoc.info displays released docs
* Documentation from master frequently confuses users