lang: Refactor most functions to support modules

This is a giant refactor to move functions into a hierarchial module
layout. While this isn't entirely implemented yet, it should work
correctly once all the import bits have landed. What's broken at the
moment is the template function, which currently doesn't understand the
period separator.

examples/lang/len0.mcl

@@ -1,9 +1,11 @@
+import "fmt"
+
 $x1 = ["a", "b", "c", "d",]
 print "print4" {
-	msg => printf("length is: %d", len($x1)),
+	msg => fmt.printf("length is: %d", len($x1)),
 }
 
 $x2 = {"a" => 1, "b" => 2, "c" => 3,}
 print "print3" {
-	msg => printf("length is: %d", len($x2)),
+	msg => fmt.printf("length is: %d", len($x2)),
 }