Example project with both windowing and command-line targets

[fractaldragonflies]

Xcode made it pretty easy to add argument-parser dependencies, but it took me awhile to figure out that I had to also argument-parser to the 'Link Binary with Libraries' element as well. Otherwise not of the argument-parser references get resolved and my project has lots of red errors!

BTW, the @main annotation in the readme.md example also errors in Xcode. Great work. Thanks.

[tscholze]

Just to bring it up again: The problem with the @main still exists in the documentation.