Add reader factory, improve tests

source/documents/scripts/reader/_factory.js.coffee

@@ -0,0 +1,11 @@
+angular.module("sideBySide").factory("readerFactory", ($injector) ->
+	return (filename) ->
+		extension = filename.split(".").pop()
+		switch extension
+			when "json"
+				return $injector.get("jsonReader")
+			when "md", "markdown"
+				return $injector.get("markdownReader")
+			else
+				throw "Unknown extension '" + extension + "'."
+)