WebSocket Application Messaging Protocol implementation for Fleck

Full WAMP implementation (incl. tests) according to http://www.wamp.ws/spec.

Note that it uses Newtonsoft.Json for serialisation/deserialisation of JSON messages as required by spec.

Added NuGet references to allow for downloading of package dependencies if they're missing during build.

Note that deserialisation of large numbers contained in messages currently doesn't work on Mono due to a missing implementation of BigInteger.Parse() on mono versions (however, according to the mono buglists, it's not far off)