Add `SLNavigationBar`.
Add `SLActionSheet`.
Add functions for comparing rects and checking rect containment to `SLGeometry.h`.

And add a missing test for `SLUIARectFromCGRect`.
Add a note to `SLTerminal+ConvenienceFunctions.h` about calling functions directly.

As opposed to calling functions using the methods defined in
the `ConvenienceFunctions` category.
Add `SLMailComposeView`.

To access and manipulate the remote view presented by `MFMailComposeViewController`.
Support loading functions that take no arguments.