fix: adding timezone support …

https://github.com/skillstream/time_splitter/pull/1/files#r16956008

https://github.com/skillstream/time_splitter/pull/2#issuecomment-54282084
Removing hardcoded assumption that time attributes will always be suffixed _at

https://github.com/skillstream/ssnext/pull/896#discussion_r17036825
Extracting valid date string logic into a method.

https://github.com/skillstream/time_splitter/pull/2#discussion_r17053538
Merge pull request #2 from skillstream/gem-refactor

fix: adding timezone support