Moved an example from pure.rst to the examples directory.

docs/examples/tutorial/pure/mymodule.pxd

+# mymodule.pxd
+
+# declare a C function as "cpdef" to export it to the module
+cdef extern from "math.h":
+    cpdef double sin(double x)

docs/examples/tutorial/pure/mymodule.py

+# mymodule.py
+
+import cython
+
+# override with Python import if not in compiled code
+if not cython.compiled:
+    from math import sin
+
+# calls sin() from math.h when compiled with Cython and math.sin() in Python
+print(sin(0))

docs/src/tutorial/pure.rst

@@ -299,25 +299,11 @@ Calling C functions
 Normally, it isn't possible to call C functions in pure Python mode as there
 is no general way to support it in normal (uncompiled) Python.  However, in
 cases where an equivalent Python function exists, this can be achieved by
-combining C function coercion with a conditional import as follows::
+combining C function coercion with a conditional import as follows:
 
-    # in mymodule.pxd:
+.. literalinclude:: ../../examples/tutorial/pure/mymodule.pxd
 
-    # declare a C function as "cpdef" to export it to the module
-    cdef extern from "math.h":
-        cpdef double sin(double x)
-
-
-    # in mymodule.py:
-
-    import cython
-
-    # override with Python import if not in compiled code
-    if not cython.compiled:
-        from math import sin
-
-    # calls sin() from math.h when compiled with Cython and math.sin() in Python
-    print(sin(0))
+.. literalinclude:: ../../examples/tutorial/pure/mymodule.py
 
 Note that the "sin" function will show up in the module namespace of "mymodule"
 here (i.e. there will be a ``mymodule.sin()`` function).  You can mark it as an