More List functionality
Allow Rails 4 libraries
Use appraisal to test against multiple dependency versions
More operations for List

Also List simply does not implement any mutation methods (e.g. map!) that cannot
be represented as atomic updates in Cassandra.
Use Range#count since Range#size is not defined in 1.9
Use Time.parse, not String#to_time

String#to_time seems to be broken in Rails 3.1