Updated README for Cocoapods.
Improvements for extensions.

Added better mechanism for defining actor shortcuts.  Provided shortcut
for setting test execution time.
More improvements for extensions.

- Convenience method for getting test target's bundle.
- Convenience methods for creating KIF errors.  (Modified code to adopt
this.)
- Added wrapper that can be used for validating KIF functionality.  (If
you are writing a test *for* KIF, you want to be able to test failure.)
- Checked in podspec.