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/text-slicer/modules/rules/html-plain-paragraphs.tid

@@ -0,0 +1,24 @@
+title: $:/plugins/tiddlywiki/text-slicer/slicer-rules/html-plain-paragraphs.json
+name: html-plain-paragraphs
+caption: Plain Paragraphs (HTML)
+description: One tiddler per paragraph, without formatting (HTML)
+type: application/json
+tags: $:/tags/text-slicer/slicer-rules
+
+[
+	{
+		"selector": "address,blockquote,center,dd,dt,h1,h2,h3,h4,h5,h6,li,p",
+		"actions": {
+			"startNewChunk": {
+				"toc-type": "paragraph"
+			},
+			"dontRenderTag": true
+		}
+	},
+	{
+		"selector": "*",
+		"actions": {
+			"dontRenderTag": true
+		}
+	}
+]