Draft: Add sphinx documentation

The mechanism for building docs was copied from EveryBeam; it parses both Doxygen documentation and python documentation into a sphinx page.

docker/ubuntu_20_04_base

@@ -34,8 +34,12 @@ RUN export DEBIAN_FRONTEND="noninteractive" && \
     && \
     ln -sf clang-tidy-12 /usr/bin/clang-tidy
 RUN python3 -m pip install \
+        breathe \
         cmake-format \
+        myst-parser \
         numpy \
         pytest \
         pytest-lazy-fixture \
-    ;
\ No newline at end of file
+        sphinx \
+        sphinx_rtd_theme \
+    ;