py-markdown-it-py: added version 2.1.0

This is a Python port of markdown-it, and some of its associated plugins.

* Follows the CommonMark spec for baseline parsing
* Configurable syntax: you can add new rules and even replace existing ones.
* Pluggable: Adds syntax extensions to extend the parser (see the plugin list).
* High speed (see our benchmarking tests)
* Safe by default

(adam)