Hey, first I want to say this crate is great. It removes a lot of pain from starting with OS dev.

I ran into a minor annoyance: mapping a large range of memory is pretty slow. In my code I'm trying to identity map all the machine's physical memory. It takes a few seconds in a release build and quite a bit longer in a debug build. I suspect a lot of this is from traversing the same tables over and over when repeatedly calling map_to.

I think methods for mapping entire ranges could be faster: instead of a loop that traverses down all levels each iteration, there could be loops at each level.

Is this a reasonable request? I'm interested in writing up a PR if it's something you'd accept.