examples: lang: Update examples to fix imports and port from yaml

Some small fixes that are useful for demos!

examples/lang/datetime3.mcl

@@ -1,5 +1,6 @@
 import "datetime"
 import "sys"
+import "example"
 
 $secplusone = datetime.now() + $ayear
 
@@ -10,7 +11,7 @@ $tmplvalues = struct{year => $secplusone, load => $theload, vumeter => $vumeter,
 
 $theload = structlookup(sys.load(), "x1")
 
-$vumeter = vumeter("====", 10, 0.9)
+$vumeter = example.vumeter("====", 10, 0.9)
 
 file "/tmp/mgmt/datetime" {
 	content => template("Now + 1 year is: {{ .year }} seconds, aka: {{ datetime_print .year }}\n\nload average: {{ .load }}\n\nvu: {{ .vumeter }}\n", $tmplvalues),