Merge remote-tracking branch 'origin/topic/awelzel/wrangling-html-theme'

* origin/topic/awelzel/wrangling-html-theme:
  conf: Add sphinx_rtd_theme to extensions, remove env based import

conf.py

@@ -141,15 +141,7 @@
 
 # -- Options for HTML output ---------------------------------------------------
 
-# The theme to use for HTML and HTML Help pages.  See the documentation for
-# a list of builtin themes.
-on_rtd = os.environ.get('READTHEDOCS', None) == 'True'
-
-if not on_rtd:
-    # only import and set the theme if we're building docs locally
-    import sphinx_rtd_theme
-    html_theme = 'sphinx_rtd_theme'
-    html_theme_path = [sphinx_rtd_theme.get_html_theme_path()]
+html_theme = 'sphinx_rtd_theme'
 
 html_last_updated_fmt = '%B %d, %Y'