fix locale using default and iOS 6+ issue
add support to seconds
add NSDate+Utils and NSString+DateUtils category
add operation and comparison function
merge branch 'new_features' into category and add instance methods
migrate to library with support to iOS and OSX
use XCTest
Merge branch 'new_features' into category
add holiday and day of week support
Merge branch 'new_features' into category
add nil check
Merge branch 'new_features' into category
fix a warning