[examples] rearrange; add hello_world.mdesk example file

examples/mdesk_files/hello_world.mdesk

@@ -0,0 +1,22 @@
+/* the hello world file */
+
+hello world!
+"hello world!"
+
+// sets
+(hello world!)
+[hello world!]
+{hello world!}
+
+// sets with labels
+hello: world!
+hello: (world!)
+
+// tags
+@exclaim "hello world"
+@message
+{
+ @recipient world
+ @contents  hello
+ @punctuate !
+}

examples/mdesk_files/node_errors.mdesk

@@ -0,0 +1,12 @@
+
+@foo @bar Foo:
+{
+    x, y, z,
+    a, b, c,
+    1, 2, 3,
+}
+
+@baz Blah:
+{
+    x100 y200 z300
+}