[ODE] Submitting documentation

[Martin C. Martin]

Hey Russ,

I'm working on some changes; I've now got joint limits and motors in the
Universal joint, and some utility functions to set a dMass if you know the
total mass rather than the density.  I'd like to clean them up and submit
them, and I figure I'd better write some simple documentation for them
too.  How do you edit the manual?  Raw HTML in a text editor?  If so, I'll
send HTML diffs.  If not, I guess I'll just send text and you'll have to
do the formatting.  Or some other format?  Just let me know.

And while we're at it, what prototype would you prefer to the "total mass"
functions?  I've been using:

void dMassSetSphereTotal (dMass *, dReal total_mass, dReal radius);

would you prefer something else?

- Martin