Minore changes in rf24 library

Signed-off-by: Andrew Andrianov <andrew@ncrmnt.org>
More rf24 refactoring

Signed-off-by: Andrew Andrianov <andrew@ncrmnt.org>
lib: Heavily refactor rf24 library:

  * Introduce queued (bulk) transfers
  * Clean up code
  * Implement hw retransmissions of failed payloads
  * Code fixes

Signed-off-by: Andrew 'Necromant' Andrianov <andrew@ncrmnt.org>
Merge branch 'rf24_refactor'