README: Add OS X specific notes about the lack of libtoolize
defensively set return-by-reference value to -1 in error condition
fix clang warning by using C99 flexible array member instead of zero length array gcc extension
suppress 64 bit truncation warning on OS X due to tv_sec being a __darwin_time_t which is a long, not an int
On gcc 4 and later, suppress the -Wcast-align warning in libusb.h
Xcode project
Add minimal config.h for Xcode

Xcode do not use ./configure so the config.h file needs to be generated
by hand.
This config.h is the minimal file for libusbx built using Xcode.
make targets for examples depend on library target.  Generate library named libusb-1.0.0.dylib not libusbx.dylib.  Added several xcconfig files to make source control and documentation easier.  Reorganised a few files' positions within the project.  Disable strict aliasing since libusbx breaks strict aliasing rules anyway. Set project format as 3.1-compatible.
added xcworkspace file since newer Xcodes freak out if its not there and recreate it anyway
added note about use of default compiler, default Mac OS X SDK, default deployment target, and default architectures.  Enabled a few more warnings.
moved a warning to release-only since gcc doesn't support it without optimizations
added some Xcode-related files to .gitignore