Add two new RPC annotations and support for buildnig an RPC communication graph.

The two annotations are:

__soaap_rpc_send("<name_of_sandbox> or <privileged>", "message_type", params...)

and

__soaap_rpc_recv("message_type", message_handler)

These are placed respectively at the points where RPCs are sent and received
respectively.

SOAAP uses these annotations to build a graph of RPC communications across security domains. The next thing to do is actually track information flow across these boundaries! These annotations have been modelled after what would be necessary for capturing RPC calls in chromium. They may be slightly changed over time to handle more general programs.

Nevertheless, I've tried to keep them as simple as possible!