Consider putting some test support code inside the segpy package

[abingham]

In developing an extension module related to segpy, I found I wanted to reuse some of the hypothesis strategies used in the segpy test suite. I'm just copying those strategies over to my project right now, but it would be nice if I could access those strategies from segpy itself. Would it be possible and/or a good idea to put e.g. any_ibm_compatible_floats into some module like segpy.testing?