DOC: first attempt at documenting load_library.

Found some doco at
http://docs.scipy.org/doc/numpy-dev/user/c-info.python-as-glue.html
which seemed to describe the function, so used that.

numpy/ctypeslib.py

@@ -89,6 +89,33 @@ def _dummy(*args, **kwds):
 
     # Adapted from Albert Strasheim
     def load_library(libname, loader_path):
+        """
+        It is possible to load a library using 
+        >>> lib = ctypes.cdll[<full_path_name>]
+
+        But there are cross-platform considerations, such as library file extensions,
+        plus the fact Windows will just load the first library it finds with that name.  
+        Numpy supplies the load_library function as a convenience.
+
+        Parameters
+        ----------
+        libname : string
+            Name of the library, which can have 'lib' as a prefix,
+            but without an extension.
+        loader_path : string
+            Where the library can be found.
+
+        Returns
+        -------
+        ctypes.cdll[libpath] : library object
+           A ctypes library object 
+
+        Raises
+        ------
+        OSError
+            If there is no library with the expected extension, or the 
+            library is defective and can't be loaded.
+        """
         if ctypes.__version__ < '1.0.1':
             import warnings
             warnings.warn("All features of ctypes interface may not work " \