Set up the interface and other files for NTDDateString Category
Test and code for shortStyleTimeStringWithCurrentLocaleFromDate: method
Refactored last test
Code for shortStyleDateStringWithCurrentLocaleFromDate

Its test was wrongly included in the last commit.
Test and code for mediumStyleDateStringWithCurrentLocaleFromDate: method
Test and code for longStyleDateStringWithCurrentLocaleFromDate: method
Updated Podspec to 1.1.0