Set rpath to include mac bundle Frameworks

[atopuzov]

Adds a LC_RPATH to executable so that libraries that use @rpath can be found in the bundle.

$ otool -l MyApp.app/Contents/MacOS/myapp
Load command ..
          cmd LC_RPATH
      cmdsize 48
         path @executable_path/../Frameworks (offset 12)

Helps with #286 (comment)

I tested this on 10.14.6 (18G6032)

[nuffsaz]

I am still having problems with @rpath (using py2app 0.28.4 with python 3.10 under MacOs 10.15.7). Is there a version of py2app available that works with @rpath? I can provide more details of what I am doing if that help. Thanks.