'git' version not compatible with Boost 1.60

[jebofponderworthy]

The stable version seems to work fine with Boost 1.60, but the 'git' version gives me the following at runtime:

TypeError: No to_python (by-value) converter found for C++ type: boost::shared_ptr<mididings::backend::BackendBase>

[dsacre]

As far as I can tell this is a bug that was introduced in Boost 1.60, and already fixed in Boost 1.61. If upgrading Boost is not an option for you, you could also apply this patch to your copy of Boost 1.60.

I'm a little surprised that the stable version of mididings would work with Boost 1.60, actually. I would have expected this bug to affect every version of mididings, since it's rather deep inside Boost.Python's C++/Python wrapping mechanism.