Merge to master (CrossNox#58)

* force mistune to version 0.8.4 (CrossNox#43)

closes CrossNox#42 
closes CrossNox#40

* pin

* Remove calls to ErrorString and SafeString removed in docutils 0.19 (CrossNox#49)

* remove python2

* fix pipelines

* fix linter pipeline

* set language for sphinx

* fix tests pipeline

* fix pipeline, set docutiles dependency

* why did I change this

* bump

* Added python_requires to setup.py (CrossNox#56)

* fix quotes

---------

Co-authored-by: Ezequiel Rosas <nhtzr.rg@gmail.com>
Co-authored-by: Ian Glen <ian@ianglen.me>
Co-authored-by: Martin Pecka <peci1@seznam.cz>

setup.py

@@ -59,4 +59,5 @@
     install_requires=install_requires,
     test_suite="tests",
     tests_require=test_requirements,
+    python_requires=">=3.7",
 )