Investigate building with "bundled" SDL2 to avoid the need to install SDL2 separately

[johnthagen]

This would allow users to not have to pre-install all of the SDL2 libraries. cargo run should just work.

See: https://github.com/Rust-SDL2/rust-sdl2#bundled-feature

[johnthagen]

This will need to be implemented in piston-music.

This is blocked until the following are completed:

• Support "bundled" feature with "gfx", "image", "mixer" and "ttf" features Rust-SDL2/rust-sdl2#778
• Use "bundled" SDL2 feature PistonDevelopers/music#74