Carthage support and section headers

[simX]

This pull request adds a framework target to support the Carthage dependency manager: https://github.com/Carthage/Carthage . This allows for the automated downloading and building of embedded frameworks for iOS 8, and Carthage doesn't modify the xcworkspace file like Cocoapods does. Building with Cocoapods is still supported, of course.

The pull request also includes some minor improvements and adds support for standard UITableView section headers in the calendar.