Improve Pan language support (#3691)

* Add a larger set of sample files for Pan

This is a fairly good cross section of Pan based on code from:
* https://github.com/quattor/template-library-examples
* https://github.com/quattor/template-library-core

* Add Pan language grammar

samples/Pan/databases.pan

@@ -0,0 +1,18 @@
+template site/databases;
+
+# Defines the mapping between the full hostname and the IP
+# address.
+final variable DB_IP = dict(
+    escape("one"), "192.168.0.24",
+    escape("hyp01"), "192.168.0.25",
+    escape("vm"), "192.168.0.26",
+);
+
+# Defines the mapping between the full hostname and the
+# physical machine.
+# A different hardware template must be used for each machine
+final variable DB_MACHINE = dict(
+    escape("one"), "hardware/machine/ibm/x3550/x_KDXXXX",
+    escape("hyp01"), "hardware/machine/ibm/hs21xm/blade_99HXXXX",
+    escape("vm"), "hardware/machine/one/example",
+);