Add plugin wrappers for async and jszip

The immediate motivation is the work I’m doing to integrate with Amazon
Web Services.

We should be able to use JSZip to export multiple tiddlers in a single
operation from the browser.

plugins/tiddlywiki/jszip/files/tiddlywiki.files

@@ -0,0 +1,20 @@
+{
+	"tiddlers": [
+		{
+			"file": "jszip.min.v2.5.0.js",
+			"fields": {
+				"type": "application/javascript",
+				"title": "$:/plugins/tiddlywiki/jszip/jszip.js",
+				"module-type": "library"
+			},
+			"prefix": "",
+			"suffix": ""
+		},{
+			"file": "LICENSE.markdown",
+			"fields": {
+				"type": "text/markdown",
+				"title": "$:/plugins/tiddlywiki/jszip/license"
+			}
+		}
+	]
+}