Added optional property objectMapper for AutoJsonRpcClientProxyCreator
Wrap null argument lists in an Object[]

Allow client interface methods to be declared with no parameters, by
creating a null Object array.
Updated wording and added link to jsonrpc 2.0 spec
Merge pull request #47 from mpcm/patch-1

Updated wording and added link to jsonrpc 2.0 spec
invocation listener
tests for the invocation listener
Merge pull request #48 from aplgithub/invocation-listener

Ability to configure an "invocation listener" in order to instrument JSON-RPC calls
Merge pull request #43 from Zetten/AllowNullArguments

Wrap null argument lists in an Object[]
Merge pull request #34 from kerlaeda/master

Added optional property objectMapper for AutoJsonRpcClientProxyCreator