Add better support for loading SDL2 mixer sounds and music from memory

[kaphula]

Adds support for loading music and sound files directly from memory regardless of their file format.

I removed the static lifetime restriction from Music and transformed it to similar function as Chunk's counterpart. This should be fine?

Fixes: #1482

How should the crate versions be updated, bump both sdl2 and sdl2-sys to 0.38.0?

[kaphula]

Okay, I can already pretty much say that the Music::from_bytes does not work like this as I managed to make it segfault. from_static_bytes needs to remain its own thing with static lifetime and from_bytes needs to use SDL_RWFromMem internally I guess. I will see if I can get it to work.

[kaphula]

I added different variants for different scenarios when Music is used from bytes.

• If music is created from a slice of bytes, then the bytes' lifetime is tied to the returned Music instance. Music::from_bytes
• If music is created from a slice of static bytes, then the bytes' lifetime is static and it is not an issue with Music. Music::from_static_bytes
• If music is created from owned bytes, then the returned Music instance takes ownership of the given bytes and drops them when the Music instance is dropped. Music::from_owned_bytes