[Fluxus] commits - interpolation order mixup

[gabor papp]

> No, looks like another twisted dave maths messup. Probably explains a
> lot of (- t)'s going on in plant eyes where I was using a lot of this.
now it has been fixed in git. it breaks old code. vmix, vlerp, lerp and 
mlerp are changed. vlerp-tangent was not working, and it was not used by 
anything, so i removed it. also added the help texts suggested by kassen.

best,
gabor