update iOS build script

1. Provides for better support of passing in the NOCODESIGN env var to
NOT codesign the build
2. Will once again codesign all of the dylibs in the modules directory
(wildcard paths passed to codesign broke in some update to Xcode)
updates to the README to reflect the new build script at libretro/libretro-super
Merge pull request #211 from maddox/updated-ios-build-script

Updated iOS build script