Use pip-tools to create the requirement file to build the docs

Docs building just broke. The requirement file had some version upper
boundary that caused problems between Sphinx and jinja2.

doc/requirements.in

@@ -0,0 +1,2 @@
+Sphinx
+sphinx-better-theme

doc/requirements.txt

@@ -1,8 +1,58 @@
-# Packages only needed to build the docs
-Pygments>=2.2,<2.3
-Sphinx>=1.6,<=1.7
-sphinx-better-theme>=0.1.5,<0.2
-
-# 0.15.2 affected by https://sourceforge.net/p/docutils/bugs/353/
-# Can update to 0.16 after release (currently in rc) but must update Sphinx too
-docutils<0.15
+#
+# This file is autogenerated by pip-compile with python 3.8
+# To update, run:
+#
+#    pip-compile requirements.in
+#
+alabaster==0.7.12
+    # via sphinx
+babel==2.9.1
+    # via sphinx
+certifi==2021.10.8
+    # via requests
+charset-normalizer==2.0.12
+    # via requests
+docutils==0.17.1
+    # via sphinx
+idna==3.3
+    # via requests
+imagesize==1.3.0
+    # via sphinx
+importlib-metadata==4.11.3
+    # via sphinx
+jinja2==3.1.1
+    # via sphinx
+markupsafe==2.1.1
+    # via jinja2
+packaging==21.3
+    # via sphinx
+pygments==2.11.2
+    # via sphinx
+pyparsing==3.0.7
+    # via packaging
+pytz==2022.1
+    # via babel
+requests==2.27.1
+    # via sphinx
+snowballstemmer==2.2.0
+    # via sphinx
+sphinx==4.4.0
+    # via -r requirements.in
+sphinx-better-theme==0.1.5
+    # via -r 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==1.26.9
+    # via requests
+zipp==3.7.0
+    # via importlib-metadata