add info_plist option in spec file for user to customize Info.plist;

Mac developers who want their apps look better in retina screen and to not run in background (and so on) must edit the Info.plist file after they built the app. Why not add the info_plist option for them to customize the Info.plist in the spec file?

    bundle = BUNDLE(exe,
      a.binaries,
      a.zipfiles,
      a.datas,
      info_plist={
        'NSPrincipalClass': 'NSApplication',
        'NSHighResolutionCapable': 'True',
        'LSBackgroundOnly': '0'
      },
      icon=None,
      name='example.app')