Add edit on github link to documentation pages

Signed-off-by: Julius Härtl <jus@bitgrid.net>

_ext/edit_on_github.py

@@ -0,0 +1,47 @@
+"""
+Sphinx extension to add ReadTheDocs-style "Edit on GitHub" links to the
+sidebar.
+Loosely based on https://github.com/astropy/astropy/pull/347
+"""
+
+import os
+import warnings
+from pprint import pprint
+
+
+__licence__ = 'BSD (3 clause)'
+
+
+def get_github_url(app, view, path):
+    return 'https://github.com/{project}/{view}/{branch}/{path}'.format(
+        project=app.config.edit_on_github_project,
+        view=view,
+        branch=app.config.edit_on_github_branch,
+        path=path)
+
+
+def html_page_context(app, pagename, templatename, context, doctree):
+    if templatename != 'page.html':
+        return
+
+    if not app.config.edit_on_github_project:
+        warnings.warn("edit_on_github_project not specified")
+        return
+
+    if not app.config.current_docs:
+        warnings.warn("current_docs not specified")
+        return
+
+    path = app.config.current_docs + '/' + os.path.relpath(doctree.get('source'), app.builder.srcdir)
+    show_url = get_github_url(app, 'blob', path)
+    edit_url = get_github_url(app, 'edit', path)
+
+    context['show_on_github_url'] = show_url
+    context['edit_on_github_url'] = edit_url
+
+
+def setup(app):
+    app.add_config_value('edit_on_github_project', '', True)
+    app.add_config_value('current_docs', '', True)
+    app.add_config_value('edit_on_github_branch', 'master', True)
+    app.connect('html-page-context', html_page_context)