Deprecate `#ignore` in favor of `#transient`

Update documentation to reflect that transient is now preferred
change file name of CONTRIBUTION_GUIDELINES.md
Add clarity around linting and database_cleaner

Closes #645
Include path to RSpec helper

Closes #648
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
Testing enum