Now computing service md5sums correctly

- Fixes #24.
- Replaces PR #22.

- Refactored the file parsing code a bit in the process; a little
  cleaner now.

Author: chfritz

index.js

@@ -203,12 +203,10 @@ let Rosnodejs = {
     var count = types.length;
     return new Promise((resolve, reject) => {
       types.forEach(function(type) {
-        messages.getServiceRequest(type, function() {
-          messages.getServiceResponse(type, function() {
-            if (--count == 0) {
-              resolve();
-            }
-          });
+        messages.getService(type, function() {
+          if (--count == 0) {
+            resolve();
+          }
         });
       });
     });