Replace SDL with minifb

[facundoolano]

This branch explores using the minifb crate instead of SDL for pixel writing and window events.

Pros:

• minifb is specifically focused on writing pixels to a framebuffer, which is the exact use case of this project.
• the API requires less boilerplate and doesn't carry the ownership issues of the rust sdl bindings (which required creating a texture manager that couldn't be passed around in structs easily). This change enabled packing most of the code in the Game and Video structs, which hint a possible path to rearranging the codebase (partially explored in this branch).

Cons:

• minifb doesn't expose primitives for writing lines and rectangles, and because of this I couldn't easily port the ray caster code that was drawing the map and rays on a separate window.
• it doesn't have sounds support, so if we ever get to that point, we'll have to look for another crate to handle that part.

The performance seems to be more or less the same as sdl (slow on debug, fast on release mode)