docs: lock docs dependencies again (acts-project#876)

Also resolve one doxygen error in the process.

See acts-project#875

docs/requirements.in

@@ -0,0 +1,7 @@
+breathe==4.30.0
+exhale==0.2.3
+m2r==0.2.1
+recommonmark==0.7.1
+sphinx==4.0.3
+sphinx_markdown_tables==0.0.15
+sphinx_rtd_theme==0.5.2

docs/requirements.txt

@@ -1,7 +1,95 @@
-sphinx>=2.0
-sphinx_rtd_theme>=0.4
-sphinx_markdown_tables
-recommonmark
-breathe==4.26.0
-exhale
-m2r
+#
+# This file is autogenerated by pip-compile with python 3.9
+# To update, run:
+#
+#    pip-compile docs/requirements.in
+#
+alabaster==0.7.12
+    # via sphinx
+babel==2.9.1
+    # via sphinx
+beautifulsoup4==4.9.3
+    # via bs4
+breathe==4.30.0
+    # via
+    #   -r docs/requirements.in
+    #   exhale
+bs4==0.0.1
+    # via exhale
+certifi==2021.5.30
+    # via requests
+chardet==4.0.0
+    # via requests
+commonmark==0.9.1
+    # via recommonmark
+docutils==0.16
+    # via
+    #   breathe
+    #   m2r
+    #   recommonmark
+    #   sphinx
+    #   sphinx-rtd-theme
+exhale==0.2.3
+    # via -r docs/requirements.in
+idna==2.10
+    # via requests
+imagesize==1.2.0
+    # via sphinx
+jinja2==3.0.1
+    # via sphinx
+lxml==4.6.3
+    # via exhale
+m2r==0.2.1
+    # via -r docs/requirements.in
+markdown==3.3.4
+    # via sphinx-markdown-tables
+markupsafe==2.0.1
+    # via jinja2
+mistune==0.8.4
+    # via m2r
+packaging==21.0
+    # via sphinx
+pygments==2.9.0
+    # via sphinx
+pyparsing==2.4.7
+    # via packaging
+pytz==2021.1
+    # via babel
+recommonmark==0.7.1
+    # via -r docs/requirements.in
+requests==2.25.1
+    # via sphinx
+six==1.16.0
+    # via exhale
+snowballstemmer==2.1.0
+    # via sphinx
+soupsieve==2.2.1
+    # via beautifulsoup4
+sphinx==4.0.3
+    # via
+    #   -r docs/requirements.in
+    #   breathe
+    #   exhale
+    #   recommonmark
+    #   sphinx-rtd-theme
+sphinx_markdown_tables==0.0.15
+    # via -r docs/requirements.in
+sphinx_rtd_theme==0.5.2
+    # via -r docs/requirements.in
+sphinxcontrib-applehelp==1.0.2
+    # via sphinx
+sphinxcontrib-devhelp==1.0.2
+    # via sphinx
+sphinxcontrib-htmlhelp==2.0.0
+    # via sphinx
+sphinxcontrib-jsmath==1.0.1
+    # via sphinx
+sphinxcontrib-qthelp==1.0.3
+    # via sphinx
+sphinxcontrib-serializinghtml==1.1.5
+    # via sphinx
+urllib3==1.26.6
+    # via requests
+
+# The following packages are considered to be unsafe in a requirements file:
+# setuptools