Callable docstrings

[mrocklin]

It appears that all callables have the callable docstring:

In [13]: nd.take?
Type:           callable
String form:    <dynd.nd.callable.callable object at 0x7fead0153870>
File:           ~/Software/anaconda/lib/python3.5/site-packages/dynd/nd/callable.so
Docstring:     
nd.callable(func, proto)

This holds a dynd nd.callable object, which represents a single typed
function. The particular abstraction this represents is still being
sorted out.

[insertinterestingnamehere]

Yep. This is a current outstanding issue that we've discussed before. Thanks for bringing it up though. Really this stems from the fact that our callable C++ objects need to have somewhere to put metadata like names and docstrings. Once that's resolved, we can expose it to Python as well.