fix "Making the release" section in ReleaseSteps documents
use clang for 3rdparty build (#92); change boost + fuego versions; general build improvements

general changes to the build
- the 3rdparty build now uses clang instead of llvm-gcc
- the clang binary used is the one reported by "xcrun"
  (instead of manually generating a deep link into the Xcode.app
  folder)
- instead of environment variables the build now uses compiler/linker
  options to specify the deployment target (e.g. -miphoneos-version-min
  instead of IPHONEOS_DEPLOYMENT_TARGET)
- the simulator build now has its own deployment target (previously
  it used the iPhone deployment target)
- remove the compiler option "-thumb-interwork" from the iPhone build
- an attempt to use the libc++ implementation of the C++ standard library
  (compiler/linker option "-stdlib=libc++") was abandoned because Fuego
  hung up on thread initialization during application startup

changes to the Boost build
- new Boost version 1.54.0 (previously 1.45.0)
- improve boost build by using the <root> option in the bjam user config
  (source for this is the Boost build script in the Gitorious project
  galbraithjosephs-boostoniphone)

changes to the Fuego build
- new Fuego version uec-cup-2013 (previously 1.1)
- fuego patch changes
  - patches 2, 3 and 4 are now consolidated in 02-fuego-mainfunction.patch
  - patch 6 that fixes a configure script problem is no longer necessary since
    the new Fuego version already contains a fixed configure script
  - new patches to fix general clang compiler errors, and C++11 compiler
    errors

doc changes
- clearly state in the quick-start guide that the build is geared to a specific
  combination of Xcode/iOS SDK
- add information about build configurations used in old version
- add detailed instructions on how a patched version of Fuego can be built
  and tested on the Mac OS X command line
add 3rdparty software as submodules

this is only the first step in a complete revamp of the 3rdparty software
build system
rewrite large parts of 3rdparty build scripts (closes #92)

change details
- software packages are now integrated as Git submodules, so
  there is no longer a need for a download phase where package
  tar balls are fetched
- the clean step is now mandatory
- removed support for Mac OS X builds
- the Boost build is now part of the Fuego build
- Boost and Fuego are now built as frameworks, the corresponding
  build scripts are part of the fuego-on-ios Git repository
- almost all build settings are now part of each software's Xcode;
  build settings in build-env.sh have been almost completely eliminated