Add travis ci (#35)

* Add travis CI
* Add ci testing of example models (with python 2.7 as py3 still fails)
diff --git a/test/model/extensions/classes/second.yml b/test/model/extensions/classes/second.yml
new file mode 100644
index 0000000..a9babd3
--- /dev/null
+++ b/test/model/extensions/classes/second.yml
@@ -0,0 +1,8 @@
+classes:
+- first
+
+parameters:
+  will:
+    warn:
+      at:
+        second: ${_param:notfound}