First pass at integrating a Markdown parser

Internal links don't work yet.

@natecain - have I included the node module in the right way?

plugins/tiddlywiki/markdown/plugin.info

@@ -0,0 +1,6 @@
+{
+	"title": "$:/plugins/tiddlywiki/markdown",
+	"description": "Markdown plugin wrapping markdown-js",
+	"author": "JeremyRuston",
+	"coreVersion": ">=5.0.0"
+}