Add Markdown syntax

This .tmLanguage file is based on what I was building for MarkDo.
I've spunt it out and plan to support MMD, Pandoc & GFM, but in a
rather loose fashion. The point of this is to be benefical to writers,
esp. when they are writing informally, as in notes, fiction, etc.
Revise Critic Markup & add Task List

& some other things
Reorder #list so that it precedes #code
Many changes, fixes, etc.

- Add UUID
- Improved Task Lists
- Improved tags
- Add support for:
	- Strikethrough
	- URLs & Emails
	- Ampersands
	- Basic HTML (hacky, currently)