[noise] A more idiomatic Rust implementation

[Trevor Perrin]

Hi Sopium,

I've been slow to improve Screech, so I'm happy to see other people
doing better rust libraries.  At first glance your code looks pretty
nice.

I sort of wanted Screech to be a zero-allocation library, but probably
the code is cleaner when you use vectors.

Anyways, you should link your library in the Noise Wiki:

https://github.com/noiseprotocol/noise_wiki/wiki

I'd like to see other people test and review it.  If we're feeling
good about your library in a few weeks I'd be happy to link it from
the Noise homepage (and remove the link to Screech, unless I'm able to
spend time on it).

Trevor