Animation - Match movement to animation speed

[timleader]

/source/games/7days/entities/animation.c

[timleader]

displacement as an input to the animation system (with a view that it will influence animation frame progression)

[timleader]

initial code is in place

[timleader]

Implement movement acceleration / velocity, is this worth doing,

Maybe immediate stop for responsiveness, yet a gradual speed when starting to move