Adding new converion that supports true heading messages (PGN 127250).

Reference is set to "True" and the Variation is set to "undefined".
The navigation.headingTrue path is used as source by default.

conversions/trueheading.js

@@ -0,0 +1,34 @@
+
+module.exports = (app, plugin) => {
+  return {
+    pgn: 127250,
+    title: 'TrueHeading (127250)',
+    optionKey: 'TRUE_HEADING',
+    keys: [
+      "navigation.headingTrue"
+    ],
+    callback: (heading) => {
+      return [{
+        pgn: 127250,
+        SID: 87,
+        Heading: heading,
+        "Variation": undefined,
+        Reference: "True"
+      }]
+    },
+    tests: [{
+      input: [ 1.35, undefined ],
+      expected: [{
+        "prio": 2,
+        "pgn": 127250,
+        "dst": 255,
+        "fields": {
+          "SID": 87,
+          "Heading": 1.35,
+          "Variation": undefined,
+          "Reference": "True"
+        }
+      }]
+    }]
+  }
+}