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/functions.pan

@@ -0,0 +1,56 @@
+################################################################################
+# This is 'namespaces/standard/pan/functions.tpl', a pan-templates's file
+################################################################################
+#
+# VERSION:    3.2.7, 21/08/09 22:22
+# AUTHOR:     Martin Bock
+# MAINTAINER: Example Maintainer <support@example.org>
+# LICENSE:    http://cern.ch/eu-datagrid/license.html
+#
+################################################################################
+# Coding style: emulate <TAB> characters with 4 spaces, thanks!
+################################################################################
+#
+# Function definitions
+#
+################################################################################
+
+declaration template pan/functions;
+
+include 'pan/types';
+
+############################################################
+##=
+## @function push
+## @# push zero or more values onto the end of a list.
+##+If the list does not exist or is not defined a new list is
+##+created.
+## @syntax value:element
+## @param:value... the values to push onto list
+## @example
+##+# "/data" will contain list (1,2,3,4)
+##+"/data" = list(1,2);
+##+"/data" = push(3,4);
+##=
+############################################################
+function push = {
+    # Get the reference to SELF or create an empty list
+    # as necessary.
+    if (exists(SELF) && is_list(SELF)) {
+        v = SELF;
+    } else if (!exists(SELF) || !is_defined(SELF)) {
+        v = list();
+    } else {
+        error("push can only be applied to a list");
+    };
+
+    # Merge the arguments into the given array.  Neither the
+    # first/next or merge functions can be used because the
+    # ARGV array cannot be directly referenced.
+    i = 0;
+    while (i < ARGC) {
+        v[length(v)] = ARGV[i];
+        i = i + 1;
+    };
+    v;
+};