Fix pydoc failure because of missing __module__

[dean0x7d]

Fixes #728.

The __module__ for all pybind11 types is set to pybind11_builtins, analogous to Python's own builtins.

[wjakob]

Looks good to me!

[wojdyr]

Maybe a shorter name for pybind11_builtins.pybind11_object_*?
Pydoc output feels a bit cluttered. For example the example from http://pybind11.readthedocs.io/en/master/classes.html#overloaded-methods is now:

class Pet(pybind11_builtins.pybind11_object_48)
 |  Method resolution order:
 |      Pet
 |      pybind11_builtins.pybind11_object_48
 |      __builtin__.object
 |  
 |  Methods defined here:
 |  
 |  __init__(...)
 |      __init__(self: example.Pet, arg0: unicode, arg1: int) -> None
 |  
 |  set(...)
 |      set(*args, **kwargs)
 |      Overloaded function.
 |      
 |      1. set(self: example.Pet, arg0: int) -> None
 |      
 |      Set the pet's age
 |      
 |      2. set(self: example.Pet, arg0: unicode) -> None
 |      
 |      Set the pet's name
 |  
 |  ----------------------------------------------------------------------
 |  Data and other attributes inherited from pybind11_builtins.pybind11_object_48:
 |  
 |  __new__ = <built-in method __new__ of pybind11_type object>
 |      T.__new__(S, ...) -> a new object with type S, a subtype of T

[jagerman]

I suppose it could be just pybind11_builtins.object_48.

It might also be nice to drop the "_48" for the default size (i.e. for the size used for a typical unique_ptr holder). So then we'd have pybind11_builtins.object typically, but the size suffix (e.g. pybind11_builtins.object_56) for other types (e.g. a type with a shared_ptr holder).

In 2.2 (with PR #693) the size suffix should be gone regardless of the holder.

[dean0x7d]

I think it would be nice to avoid shadowing builtin names like object and type. While they are formally in the __builtin__ (2.7) / builtins (3.x) modules, the objects are always available unqualified globally. I don't think that shadowing them would be too much of a technical issue, but perhaps confusing upon user inspection, especially as Python 2.7 uses unqualified names. E.g. looking up type(A).__name__ for a pybind11 class and seeing type just like a regular Python class may lead someone to the wrong conclusion while debugging. Similarly for bases and object.

That said, I'm not attached to the pybind11_-prefix-everywhere naming scheme and don't mind a bit of bikeshedding on this, just without shadowing the builtins. Note that __module__ == "" is a possibility, I just didn't go for it here because pydoc leaves the dot prefix anyway.