Default Sprite Behaviors: KeyBoardMovementSprite

[pathunstrom]

In the interest of improving the on-boarding ramp for new users and learners, and by extension making our live demonstrations a little more impressive, we'd like to include some Sprites with basic control features.

For this ticket we are defining a KeyboardMovementSprite. This sprite should allow you to move the object with four directional keys defined by the developer. The default should be the arrow keys, and we should define a module attribute for WASD movement. Other layouts will require definition from the end user.

We'd like to provide a collection of movement strategies: various kinds of linear interpolation and a basic physics model with a velocity, acceleration and max velocity.

This sprite will almost definitely need to be subclassed to add behaviors for the end user.