Do not alter archives during installation.

Replacing the archives can lead to corrupt archives and subsequent ranlib failure. Fixes Issue #5.
Fix error "No architectures to compile for (ONLY_ACTIVE_ARCH=YES, active
arch=x86_64, VALID_ARCHS=i386)."
Clarify xcconfig installation instructions
ghc-ios script can pass arguments to ghc commands
Not sure when setting this variable is neccesary.
Clean up example
Merge branch 'master' of https://github.com/angerman/ghc-ios-scripts

Fix error: size too large (archive member extends past the end of the file)
Merge pull request #12 from asivitz/master

Make ghc-ios act more like ghc command