Mono support

Added Mono support
* Updated Newtonsoft.Json.dll library to the latest v4.0
* Added Mono.Posix.dll
* Added reference to System.Numerics. This assembly is required for Newtonsoft, but it's not included in Mono installation.

Works fine on Ubuntu. Make sure you copy System.Numberics.dll to Linux machine. Copying Mono.Posix.dll is not required - it's included just as a reference.