Add subdirectory also to :doc: reference definitions

Fixes #168.

Author: mgeier

doc/subdir/a-notebook-in-a-subdir.ipynb

@@ -42,6 +42,8 @@
     "\n",
     "</div>\n",
     "\n",
+    "A link to a notebook in the same sub-directory: [link](toctree.ipynb).\n",
+    "\n",
     "A link to a notebook in the parent directory: [link](../markdown-cells.ipynb).\n",
     "\n",
     "A link to a local file: [link](../images/notebook_icon.png).\n",

src/nbsphinx.py

@@ -1076,10 +1076,8 @@ def apply(self):
             target_docname = nbconvert.filters.posix_path(os.path.normpath(
                 os.path.join(os.path.dirname(env.docname), target)))
             if target_docname in env.found_docs:
-                if target_ext:
-                    target = target_docname + target_ext
-                    target = target.lower()
-                target = '/' + target
+                target = target_docname + target_ext
+                target = '/' + target.lower()
                 linktext = node.astext()
                 xref = sphinx.addnodes.pending_xref(
                     reftype=reftype, reftarget=target, refdomain=refdomain,