textproc/py-marko: Add py-marko 1.1.0

Marko is a markdown parser written in pure Python that complies with
CommonMark's spec v0.30. It is designed to be highly extensible.

Among all implementations of Python's markdown parser, it is a common issue that
user can't easily extend it to add his own features. Furthermore,
Python-Markdown and mistune don't comply with CommonMark's spec. It is a good
reason for me to develop a new markdown parser.

Respecting that Marko complies with CommonMark's spec at the same time, which is
a super complicated spec, Marko's performance will be affected. However, using a
parser which doesn't comply with the CommonMark spec may give you unexpected
rendered results from time to time. A benchmark result shows that Marko is 3
times slower than Python-Markdown, but a bit faster than Commonmark-py, much
slower than mistune. If performance is a bigger concern to you than spec
compliance, you'd better choose another parser.

WWW: https://github.com/frostming/marko