Exposes blocking() via server constructor

[ssimeonov]

Per the README, blocking() should be exposed by the server constructor function and not the instance objects. This makes sense for two reasons:

1. Developers should be able to define RPC methods prior to a server instance being created.
2. The implementation has no dependencies on the server instance.

[Raynos]

Can we add it to both and leave a comment that the prototype version is deprecated.

Although @dfellis might want to chip in and say that we can just remove the prototype method.

[dfellis]

So we've never actually used the blocking method in any of our prod code, but this is a public repo so we should either deprecate it or publish 0.5.0 after this. I'd rather not do a bigger version bump for a one-liner that probably doesn't affect anyone else's code out there, so can we leave it in both and make a note in the readme that getting the blocking method off of an instantiated server is deprecated?