Document G5, G5.1, G5.2, G5.3 NURBS/spline commands

This should close bug #369.
Merge remote-tracking branch 'origin/v2.5_branch' into 2.6
add driver for the 7i90

This is almost entirely a copy of the 7i43 driver, with a few tiny tweaks.
Should be integrated with the 7i43 driver so they share more code,
but that can happen in the master branch later.