Pitch data constructor

[webern]

Closes #69

[webern]

There is something horrible about MSVC 19.25.28614.0 and I don't have time to chase it down. It's possible that there's undefined behavior in the mx code, but the last time I chased a Windows crash I ended up here: https://developercommunity.visualstudio.com/content/problem/847490/msvc-codegen-error-vector-reverse-iterator-x64-c17.html

The fix for mx was basically 'move something around so the buggy compiler doesn't make bad code'

#61 had the fix and it was here: https://github.com/webern/mx/blob/20796cd4638b8beec6f7833c436a7e267a5699c1/Sourcecode/private/mx/core/ElementInterface.cpp#L142...L150