Major updates to text-slicer plugin

* In the interests of performance and expressiveness, switched to using a Sax parser instead of a DOM implementation.
* Use extensible declarative rules to control the slicing process
* Added new optional set of rules for slicing by heading, where the paragraphs underneath a heading are packed into the same tiddler as the heading
* Added a modal dialogue for specifying parameters when slicing in the browser

plugins/tiddlywiki/sax/plugin.info

@@ -0,0 +1,7 @@
+{
+	"title": "$:/plugins/tiddlywiki/sax",
+	"description": "Wrapper for sax.js library by Isaac Z. Schlueter",
+	"author": "Isaac Z. Schlueter",
+	"core-version": ">=5.0.0",
+	"list": "readme license"
+}