Request specific sphinx version otherwise RTD build fails. Use readth…

…edocs.yml to request python version

readthedocs.yml

@@ -0,0 +1,26 @@
+# readthedocs.yml
+# Read the Docs configuration file
+# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
+
+# Required
+version: 2
+
+# Build documentation in the docs/ directory with Sphinx
+sphinx:
+  configuration: docs/conf.py
+
+# Build documentation with MkDocs
+#mkdocs:
+#  configuration: mkdocs.yml
+
+# Optionally build your docs in additional formats such as PDF and ePub
+formats: all
+
+# Optionally set the version of Python and requirements required to build your docs
+python:
+  version: 3.7
+  install:
+    - requirements: requirements.txt
+
+submodules:
+  include: all

requirements.txt

@@ -1,3 +1,3 @@
-sphinx
+sphinx>=2.4.3
+breathe>=4.14.1
 sphinx-rtd-theme
-breathe