Remove Buildout and just use `pip` to genrate the Sphinx docs

Makefile

@@ -226,13 +226,10 @@ test:
 ./bin/activate:
 	python3 -m venv .
 
-.installed.cfg: requirements.txt buildout.cfg
-	./bin/pip install -r requirements.txt
+.PHONY: docsdev
+docsdev: ./bin/activate requirements.txt
 	./bin/pip install --upgrade pip==21.3.1
-	./bin/pip install --upgrade setuptools==51.3.3
-	./bin/buildout -v
-
-docsdev: ./bin/activate .installed.cfg
+	./bin/pip install -r requirements.txt
 
 .PHONY: html
 html: doc

buildout.cfg

@@ -1,15 +0,0 @@
-[buildout]
-parts =
-    sphinx
-
-versions = versions
-
-[sphinx]
-recipe = zc.recipe.egg
-eggs =
-    Sphinx
-    sphinx-bootstrap-theme
-
-[versions]
-Sphinx = 4.5.0
-docutils = 0.17.1

requirements.txt

@@ -1 +1,3 @@
-zc.buildout==2.13.6
+Sphinx==4.5.0
+docutils==0.17.1
+sphinx-bootstrap-theme==0.8.1