- OutputBuffer retracts all remaining live IUs on destruction
- sends correct event type now
- fixed reference error for calling handlers
- setters properly check for retracted flag
- also added some missing checks for committed flag

Also removed stray cout lines

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

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

Also changed constructors of PayloadEntryProxy to protected.

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.

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)

It is Herwin's resend fix. Test sources are present but not
enabled during library build (will have to implement test build asap).