* chore: update deprecated import from collections

* chore: remove outdated imports from markdown library

as it hasn't been supported since 2.0.3 and we're on 3.x.
This was deprecated at least as early as 2012!

* docs: add docstring and remove lint-amnesty to markdown plugin

* chore: remove deprecated etree import

* style: remove unnecessary-comprehension for sets

* style: resolve a number of amnestied pylint complaints

Co-authored-by: stvn <stvn@mit.edu>