Add stub support for streaming RPC APIs.

Testing : precheckin --full --strict-errors
Reviewer: Fare (please)

JTB impact: No
Ops impact: No

Change to config                        : No
Change to XML schema                    : No
Change to DB schema                     : No
Change to transport (timeouts, headers) : No
Any change (or new use) of OAQs         : No
Change to inter-component transactions  : No
Depends on any other checkin / bug      : No

Tests that will verify:

I extended the CL-Protobufs tests

Description:

Add support for a 'streams' type in Protobufs RPC methods.
 - Add a few slots to 'protobufs-method'
 - Add '&key streams' to the method arglists in 'define-service'
 - Extend the parser to handle "streams" in addition to the
   'streams_type' option
 - Extend the printer
 - Change a test to use a 'streams' type
 - While we're in the neighborhood, allow an optional '=>'
   between the input and output methods in 'define-service';
   it makes it a bit more readable
 - Update the documentation



git-svn-id: http://svn.internal.itasoftware.com/svn/ita/trunk/qres/lisp/libs/cl-protobufs@560147 f8382938-511b-0410-9cdd-bb47b084005c