ENH: add .path property to Dataset providing local path to cache (#25)

* ENH: add .path property to Dataset providing local path to cache

* docs

* fix api docs

Author: martinfleis

doc/source/api.rst

@@ -27,7 +27,8 @@ Database-level API
 
 The database of dataset metadata is handled via custom dict-based classes.
 
-.. class:: Dataset
+.. autoclass:: Dataset
+   :members: path
 
    A dict with attribute-access and that can be called to update keys.