Port from std to alloc, excluding stdout

[hegza]

I thought this was useful for testing on bare metal RISC-V, so I ported it to work without std using alloc only. Anything to do with printing to stdout was left out of the alloc version, since that's strictly a part of the standard library.

Level of testing:

• cargo test passes as in original
• the 'alloc' version checks out with cargo check --no-default-features --features=alloc

[yonkeltron]

Hey thanks for opening this, we're reviewing it right now and will get back to you. In the meantime, know that you have our gratitude for your involvement and initiative!

Thanks, +Jonathan

[yonkeltron]

Hey are you still interested in getting this merged in?

[hegza]

Yeah, sure. What do I need to do?