Add deps for nbconvert to HTML for 'notebook' target

Also, nbconvert no longer requires Sphinx.

setup.py

@@ -273,8 +273,8 b' extras_require = dict('
     test = ['nose>=0.10.1'],
     terminal = [],
     nbformat = ['jsonschema>=2.0', 'jsonpointer>=1.3'],
-    notebook = ['tornado>=3.1', 'pyzmq>=2.1.11', 'jinja2'],
-    nbconvert = ['pygments', 'jinja2', 'Sphinx>=0.3', 'mistune']
+    notebook = ['tornado>=3.1', 'pyzmq>=2.1.11', 'jinja2', 'pygments', 'mistune'],
+    nbconvert = ['pygments', 'jinja2', 'mistune']
 )
 
 if sys.version_info < (3, 3):