Fix "Edit on Github" links (#577)

Fix the "Edit on Github" links by removing the
`_templates/breadcrumbs.html` file: Sphinx and the RTD theme can
generate those links if the docs are correctly configured.
Add `"conf_py_path"` to the `html_context` dictionary in Sphinx
configuration file, so the links to the source files work correctly.
Minor updates on the configuration file to avoid some warnings: remove
the `language=None` and `html_theme_path`.

conf.py

@@ -78,13 +78,6 @@
 # The full version, including alpha/beta/rc tags.
 release = '0.0.5'
 
-# The language for content autogenerated by Sphinx. Refer to documentation
-# for a list of supported languages.
-#
-# This is also used if you do content translation via gettext catalogs.
-# Usually you set "language" from the command line for these cases.
-language = None
-
 # There are two options for replacing |today|: either, you set today to some
 # non-false value, then it is used:
 #today = ''
@@ -164,12 +157,12 @@
 
 import sphinx_rtd_theme
 html_theme = 'sphinx_rtd_theme'
-html_theme_path = [sphinx_rtd_theme.get_html_theme_path()]
 html_context = {
   'display_github': True,
   'github_user': 'geoscixyz',
   'github_repo': 'em',
-  'github_version': 'main'
+  'github_version': 'main',
+  "conf_py_path": "/", # Path in the checkout to the docs root
 }
 # The name for this set of Sphinx documents.  If None, it defaults to
 # "<project> v<release> documentation".