Upgrade to new ReadTheDocs system (#744)

- Fixate new settings in .readthedocs.yaml
- Pin on Ubuntu 22.04
- Upgrade to Python 2.7
- Explicitly move to Xetex  engine

Reviewed-on: https://git.door43.org/unfoldingWord/en_uhg/pulls/744
Co-authored-by: Jakob Aleksandrovich <jakobaleksandrovich@gmail.com>
Co-committed-by: Jakob Aleksandrovich <jakobaleksandrovich@gmail.com>

.readthedocs.yaml

@@ -1,5 +1,11 @@
 version: 2
 
+# Build settings
+build:
+  os: "ubuntu-22.04"
+  tools:
+    python: "3.7"
+
 # Build documentation in the docs/ directory with Sphinx
 sphinx:
    configuration: content/conf.py
@@ -12,7 +18,6 @@ formats:
 
 # Optionally set the version of Python and requirements required to build your docs
 python:
-  version: "3.7"
   install:
   - requirements: docs/requirements.txt
 

content/conf.py

@@ -240,6 +240,9 @@ htmlhelp_basename = 'UHG'
 
 # -- Options for LaTeX output ---------------------------------------------
 
+# Use XeLaTex (to properly handle Unicode)
+latex_engine = 'xelatex'
+
 latex_elements = {
      # The paper size ('letterpaper' or 'a4paper').
      #

docs/requirements.txt

@@ -1 +1,2 @@
 docutils<0.18
+sphinx-rtd-theme==1.3.0