Major revisions to Modbus analyzer support (not quite done yet).

- Renamed many data structures to align with most recent standard.

- Reworked modbus events to make them more canonically "Bro".

- Converted the Modbus analyzer to a simpler style for easier maintenance.

- Modbus coil related events still don't work (I haven't finished the
  function for converting the data structures).

- Modbus file record events remain incomplete.

src/types.bif

@@ -156,6 +156,13 @@ type readdir_reply_t: record;
 
 type fsstat_t: record;
 
+
+module GLOBAL;
+
+type ModbusHeaders: record;
+type ModbusCoils: vector;
+type ModbusRegisters: vector;
+
 module Log;
 
 enum Writer %{