Improved coding style of OS X implementation

And fixed some typos.
Fixed a few glitches in the documentation
Fixed unused parameter warnings
Removed support for OS X 10.6 and below
Updated Objective-C implementation to use ARC; removed i386 support
Fixed NSApplication not retaining its delegate
Added some memory autorelease pools and nil'ify attribute
Fixed incorrect symlink in freetype.framework (close #519)
Added support for OpenGL 3.2 context on OS X (close #84)

The Graphics module is not compatible with a core profile on Mac. If
you plan to use it, use OpenGL 2.1 (default).
Updated Xcode templates and cmake script

What's new in the templates:
 - Removed support for 32 bits and gcc
 - Removed useless code
 - Removed custom warnings settings – let Xcode decide with its default values
 - Set default target version to CMAKE_OSX_DEPLOYMENT_TARGET

What's new in cmake script:
 - Added cmake options for archs and deployment target
 - Added minimum requirements checking