(Replace std::vec w/ std::slice for compatibility w/ latest master.)
(Shhh... I'll learn to hate tabs eventually.)
Moves strobing test into sepaate function to visually declutter `#draw()`
Fixes whitepsace in `src/player.rs`
Fixes whitespace in `sprite.rs`
Fixes whitespace in `map.rs`
Fixes whitespace in `input.rs`
Fix whitespace in `src/graphics.rs`
Fix whitespace in `src/game.rs`
Fix whitespace in `src/collisions.rs`
Fix whitespace in `src/backdrop.rs`
Fix whitespace in `units` module
Fix whitespace in `enemies` module
Merge branch 'exp/fix-whitespace'

This fixes up some whitespace errors & issues in this project.

* Trailing commas added to paramter lists & structure definitions.
* Hard tabs are only used at line-beginnings
* Soft tabs are used to align struct elements & argument lists.
* Some multiline continuations have been cleaned up.
(Update dep on `rust-sdl2`)
Convert some `Freeze` bounds to new `Share` bound.

To continue stuffing sprites inside RWArc the type-system must
guarantee that they impl. the `Share` trait.
(Project maint.)