[GI#2] Add podspec.
[GI#2] Update podspec commit reference.
[GI#2] Adopt semantic versioning.
[GI#2] Include resources in Podfile.
Add changelog.
Merge pull request #4 from modocache/feature/podspec

[GI#2] Add podspec.
Update copyright.
Only instantiate date formatters once.
Only instantiate NSCalendar once.
Update LICENSE.