JSON files can now have file references

To add a file references put a string property in with an
@file_name value (see the following example).

{
"file_ref": "@file_name"
}
Merge pull request #13 from DeVaukz/develop

OS X fixes
added simple post process support
Updated assets and some CMake files

The cmake changes are need on Windows where explicit paths are set.
Fix the varying names for DEFAULT_TARGETS