Add stubs for pure and directives.

src/reference/directives.rst

+Compiler Directives
+===================
+
+TODO. See http://wiki.cython.org/enhancements/compilerdirectives
\ No newline at end of file

src/reference/index.rst

@@ -16,6 +16,7 @@ Contents:
    interfacing_with_other_code
    special_mention
    limitations
+   directives
 
 Indices and tables
 ------------------

src/tutorial/index.rst

 Tutorials
 =========
 
-Contents:
-
 .. toctree::
    :maxdepth: 2
 
@@ -14,6 +12,7 @@ Contents:
    profiling_tutorial
    numpy
    strings
+   pure
    readings
    related_work
    appendix

src/tutorial/pure.rst

+Pure Python Mode
+================
+
+TODO: http://wiki.cython.org/pure
\ No newline at end of file