Merge tag '4.0.3' into develop

Version 4.0.3

* Update supported Python versions to 3.8 - 3.12 [#83](#83)
* Replace html5lib with nh3 for html sanitization
* General code cleanup
* Bugfixes:
**  Wrong HTML output when "bc.." is the very last in the document [#81](#81)
* Other:
** Use github actions instead of travis for automated testing

Author: ikirudennis

Makefile

@@ -1,6 +1,6 @@
 clean:
-	rm README.txt
-	rm -rf ./dist ./build
+	$(RM) README.txt
+	$(RM) -r ./dist ./build
 
 generate_pypi_README:
 	${VIRTUAL_ENV}/bin/pytextile README.textile | sed -e 's/^\t//' > README.txt

textile/version.py

@@ -1 +1 @@
-VERSION = '4.0.2'
+VERSION = '4.0.3'