Manually integrated the following changes from b8466a (master 2015-11-13)

- Blackboard classes by hvanwelbergen
- Blackboard test by hvanwelbergen
- Payload merge fix by hvanwelbergen
- rsb Buffer fix (by myself) copied but inactive (not needed atm?)

Please refer to the logs of the legacy-str branch for a full history
of the respective changes.

Use with Locker, possible in a dedicated stack frame, like this:
// ... code ...
{ // open stack frame
	Locker locker(iu->payload());
	iu->payload()["a"] = "string";
	iu->payload()["b"] = "simultaneouslySentString";
} // close stack frame, sending the update

(by ignoring nonexistent keys)

Also renamed some functions (preserving old names as deprecated aliases)

Also changed constructors of PayloadEntryProxy to protected.

Create doxygen documentation thus:
$ cd docs
$ doxygen ipaacaCpp.Doxyfile

Address mode must be selected explicitly using as_map/as_list, like so:
  for (auto value: iu->payload()["listItem"].as_list()) { .... }
  for (auto kv_pair: iu->payload()["mapItem"].as_map()) { .... }
Generic size() function (reports 0 for non-structured types)

PayloadTypeConversionError thrown if (trimmed) string parse is
incomplete; comparison operators == and != catch this error though.

(This was sufficient for basic interoperation, e.g. DM<->realizer)

Setting default channel name and default payload type works OK

Sniffer: only display quotes for string-type payload values
Injector: using unicode() and catching errors

TODO: compatibility with STR legacy payloads; more varied
access to inner payload objects (e.g. push_back)

(for remotely triggered local-IU handlers, in order to let the
RPC call of the remote side succeed as it should).