message: CMake change to restore Read The Docs html theme.
  During recent BLT cleanup, this was removed from BLT because it was Axom specific
  and not added to Axom.
diff: # documentation targets
  ################################
  +set(SPHINX_HTML_THEME "
  +try:
  + import sphinx_rtd_theme
  +except:
  + html_theme = 'classic'
  + html_theme_options = {
  + 'codebgcolor': 'lightgrey',
  + 'stickysidebar': 'true'
  + }
  + html_theme_path = []
  +else:
  + html_theme = 'sphinx_rtd_theme'
  + html_theme_options = {}
  + html_theme_path = [sphinx_rtd_theme.get_html_theme_path()]
  +")
  +
  add_subdirectory(web_main)
  add_subdirectory(coding_guide)
  add_subdirectory(dev_guide)
  