Use `Result` rather than `Maybe` for texture loading

[abingham]

Right when a texture fails to load for some reason, we can't tell why it failed because we just get a Nothing. Could you change this API to use a Result Http.Error Texture or even just a Result String Texture describing the failure?

[abingham]

I could probably put some work into a PR on this, but I'd first like to know if it's likely to be accepted.