Difference in `from_rotation_y` between `0.7` and `0.8`

[kovaxis]

Noticed that in 0.7, from_rotation_y rotated around the -Y axis, but it now rotates around the +Y axis, in a right-handed coordinate system. I like the new behaviour, it's a lot more intuitive, but it would be nice to document this change, it took me a while to figure out what was going wrong.

I believe this is related to #130.