Simplistic registry to aid in endpoint negotiation

updated serial to take advantage, (minimally) refactored rf12demodecode to take advantage of "instancing" of tags.
(housemon/rf12demodecode PULL to come behind this.) <--done (see my hm 0.9-endpoint-registry branch)

Please try it out, I use (a version) of this successfully, that adds features such as TTL reaping of endpoints etc, but kept that back for now as dont want to be accused of feature creep 

Key features of this are:-
Simplistic client registration (almost all hidden). Pretty generic, can be used by other input systems. Can easily expand to handle non-line orientated devices via better endpoint control. One you have registered, it sits out the way (this version does not watch anything).

In a nutshell, send mqtt message to register, await a response, use endpoint+timestamp to write, listen on endpoint for read (from standpoint of device).
Guaranteed to get a structured endpoint of format: 
```
<root>/<tag>/<taginst>
```
Most things are defined with constants/runtime changeable data.
Can be used from "consumers" of jeebus package.

Also, if data providers stick to the:
```
<rootspace>/<tag>/<taginst> 
```
concept (i.e small devices that can process message/response for reg) they they can also continue within system, although they would be responsible for the <taginst> collision avoidance.