Replace "latest" specs with redirect stubs

Jekyll can't do HTTP redirects, but this causes it to generate
HTML files with a meta redirect tag, which is close enough as these
are probably almost always accessed through browsers.

Author: handrews

latest/json-schema-core.html

@@ -0,0 +1,5 @@
+---
+redirect_to: "/draft/2019-09/json-schema-core.html"
+title: "JSON Schema: A Media Type for Describing JSON Documents"
+---
+