Expose BufferError among other pybind11 exceptions

[mosra]

A very minor thing, exposing python's BufferError among other exception types. Useful when dealing with py::buffer_protocol{} interfaces. Not sure if any tests need to be added for this, I guess not :)

Thank you!

[wjakob]

This looks fine. For posterity, can you give an example of a potential use case that involves throwing a hypothetical py::buffer_error from C++?

[mosra]

Is a link to another repo fine? This is one use case: https://github.com/mosra/magnum-bindings/blob/1ec72697322715ce1d79cdd2eb22f11c1a6fc0af/src/python/corrade/containers.cpp#L121-L122

 if(buffer.strides && buffer.strides[0] != buffer.itemsize)
    throw py::buffer_error{Utility::formatString("expected stride of {} but got {}", 
        buffer.itemsize, buffer.strides[0])};

Basically, any error handling in py::init() that takes a py::buffer, or in in a def_buffer() would be throwing these.

[wjakob]

Ok, sounds good :)