Remove separate definitions header files, and use #if TARGET_OS_IPHONE.

It is no longer necessary to import only the correct definitions file. The preprocess conditions sort it out.
Remove entries I don’t find useful from gitignore, and add one I do.
Consolidate the examples into a single Xcode project and modernise the examples a little.

Separate projects are not necessary now cross platform support does not rely on two different files with the same name.
The OS X example now skips Core Data, and saves the randomly generated points.
Use consistent source file preamble and module-style imports, and slightly tidy up the iOS example.
Use value label attributes instead of separate font and colour properties.

Platform distinctions for string measuring and drawings are no longer needed.
Fixes deprecation warnings on iOS.