Added build.sh script to compile a universal library for iOS

## Build iOS static library ##

Execute `build.sh` to compile a universal library for iOS simulator/device. The produced library and header files are located at `build/Release-iphone`. You may also change the version of iOS SDK by specifying `IOSSDK_VER` in the `build.sh` (all available versions can be found using `xcodebuild -showsdks`).