ent: measuring entropy

good review for me...

from a file or stdin, measure the Shannon entropy of the bytes.

reproduction of https://github.com/lsauer/entropy/, but from first principles (clean-room) and in Rust

clap is a bit heavy of a dep for this executable, find a lighter argparse (b/c i don wanna do argparsing myself unless I have to).

i wanna make rent, so r-ent is a convenient project name...

Installation

From crates.io:

cargo install r-ent

Locally:

git clone https://git.sr.ht/~jangermad/r-ent
cd r-ent
cargo install --path . --locked