Multiple frames (#8)

* Add fields to mmr header

* Reorder priority constants

* Add message priority

* Add header to message

* Fix compile error

* Set correct bits in header

* Refactor

* Create queue

Inc/mmr_can.h

@@ -78,7 +78,7 @@ typedef struct {
  * Represents a CAN message
  */
 typedef struct {
-  CanId senderId;
+  MmrCanHeader header;
   void *store;
 } MmrCanMessage;