C++ Rest SDK - JSON library

This JSON library is taken from the C++ REST SDK in https://github.com/microsoft/cpprestsdk

Based in the v2.10.13 release, it consists of the needed files to build and use the JSON classes described in include/cpprest/json.h.

Changes made to the files in order to build in the PowerToys project:

• Removal of #include references to files that are not needed.
• #include "pch.h" instead of #include "stdafx.h" to use the PowerToys pre-compiled header.
• #define _NO_ASYNCRTIMP in include/cpprest/details/cpprest_compat.h since this class will be statically linked.

The contents of the C++ Rest SDK license are included in license.txt.