Fixed #179 add Flask-Caching

requirements/dev.txt

@@ -177,10 +177,11 @@ mako==1.1.4
     # via alembic
 markdown==3.3.4
     # via plantuml-markdown
-markupsafe==2.0.0
+markupsafe==1.1.1
     # via
     #   jinja2
     #   mako
+    #   sphinx
     #   wtforms
 matplotlib==3.4.2
     # via statisticaldiagrams
@@ -370,7 +371,7 @@ snowballstemmer==2.1.0
     # via sphinx
 speaklater==1.3
     # via -r requirements/docs.in
-sphinx==3.4.3
+sphinx==4.0.1
     # via
     #   -r requirements/docs.in
     #   sphinxcontrib-github