Performance improvements

Thanks to everyone who filled out the survey. It's given me a good idea what to build next... starting with this performance improvements release. The survey is still open if you want to help shape this project. Class support is my next focus.

Release notes:

• Reduces the overall memory footprint.
• Improves resolving performance and caches already resolved items.
• Improves performance of indenting the generated code.
• Efficiently removes and inserts code, greatly shortening the time to generate a nested test double class.
• Indents code using tabs or spaces defined in your Xcode project.