Add new directions & sprites
Consolidate `last motion` logic to `current_motion` and `set_facing` methods.
Documented `player.rs`
Start of SDL 2 conversion
Fully match tuple for Key<Up,Down>Event's
Changes to use Rc & Textures
Remove Send bound on ~sprite::Updatable box

This allows me to box a sprite polymorphically even though it contains an Rc<Surface>
As a note to self: these textures _must live_ w/ the task responsible for rendering.
(If I ever impl. a multi-threaded pipeline.)
Last minute tweaking on render settings