Xcode 13 Compatibility and Doing Validation Eariler

[insha]

The fix for issues #66 and #67 is accomplished by extracting the project setting logic into its own class and using a closure to defer processing until project settings have been validated.

The fix for #82 is fairly straight forward and only the set needed to be updated to include "Xcode 13.0".

This also adds a git ignore file.

Closes #82 Closes #67 Closes #66

[dempseyatgithub]

Thanks for your work on this @insha!

I haven't had a chance to review the bulk of your PR in doing the validation earlier, but I will get to it the next time I am focusing on doing some improvements.

In the meantime, I'm going to do a separate commit for Xcode 13.