can add a new function call: NewtonbodyAddAcceleration()

[chankahou]

is there any function about added gravity directly
because in "NewtonBodySetForceAndTorqueCallback" callback function
i always use "NewtonBodyAddForce" to apply the gravity: mass*-9.8

so i want some function can by included in this library like:
NewtonbodyAddAcceleration(body, gravity);

thank for the good physics engine~

[JernejL]

Acceleration is a result of adding force.

Adding that would mean supporting pure lazyness. It's no different to if you made this function yourself.