Add RVC Spec decoder versioning info

Author: greendog99

HOW_IT_WORKS.md

@@ -103,6 +103,13 @@ to the MQTT bus:
 }
 ```
 
+Since other tools use the mqtt outputs of the script, the decoder spec
+is versioned so that any changes to the output can be tracked and
+downstream scripts can be updated.
+
+`rvc2mqtt.pl` publishes (and retains) the current API version on mqtt
+topic `RVC/API_VERSION`.
+
 Sending RV-C Messages to CANbus
 -----------------------------------
 

roles/coachproxy/files/etc/rvc-spec.yml

@@ -20,7 +20,7 @@
 # a name from lower case to upper case, can have an impact on tools
 # that have been written to use the mqtt output generated from this
 # spec file.
-API_VERSION: 0
+API_VERSION: 1
 
 17F00:
   name: GENERAL_RESET