Store coordinate spaces

[io7m]

Store coordinate spaces in skeleton files in the same manner as io7m-com/smfj#2.

[io7m]

The mathematics in the package assumes a right-handed coordinate system.

It's possible that the specification could require explicit storage of coordinate space information, but the implementation will only support right-handed -Z forward.

[io7m]

This is something the Blender plugin will need to be able to produce, and the skeleton compiler able to evaluate.

[io7m]

Additionally: What does a program do if it loads a compiled skeleton and finds out that the coordinate system doesn't match what it requires?