Make MQTT wildcard subscriptions possible

I need wildcard subscriptions for a project but I'm happy with just filtering the topics myself.

So here is a "minimal effort"-solution, at least as a discussion starter.

It only works with the binary_multipart_messages as they are the lowest-level end of subscribing atm.

The solution is as following: On every message we look if there are any handlers with topics containing a wildcard registered. Each of them gets the message and they have to match the topics on their own.

This:

• doesn't impede the regular handlers like our OTA handler
• doesn't break anything else as wildcard handlers won't ever be called atm because you can't publish messages with wildcards in their topics

Other solutions are:

• implement a full-blown topic matching algorithm and despatch the messages correctly like paho-mqtt does on bigger computers