Use ring buffer and semaphore

[Locke]

This PR is based on UrbaneChimp/433Utils@3f2517e, I only did the porting.

I basically have the issue mentioned in ninjablocks/433Utils#16. @rotv pointed out that there is a fork with a solution which could be applied here (as ninjablocks/433Utils#17 is merged by now). Actually there are a few more forks containing that solution and it appears none has brought it up here.

I tested these changes with a small change to the 433Utils on a raspberry pi: https://github.com/Locke/433Utils/blob/popEvent/RPi_utils/RFSniffer.cpp

My biggest concern is that this pulls in another dependency which might not be available / suited for the Arduino. I can imagine using flags to enable these changes only for the RPI or via a new flag.

[Locke]

My biggest concern is that this pulls in another dependency which might not be available / suited for the Arduino. I can imagine using flags to enable these changes only for the RPI or via a new flag.

My feeling was right. I read a bit about Arduino and multitasking and understand now that this approach doesn't make sense for the Arduino. (Even if you use something like ArduinoThread to schedule tasks you would check .available() and not "block a thread".)

I'm not sure what the best approach is to control this via flags. Add a RCSwitchEnableBlockingReceive flag and enable it by default for the RPI? Any other suggestions?

[Locke]

I added the RCSwitchEnableBlockingReceive flag. It will be defined when RPI is defined, unless RCSwitchDisableReceiving is set.