C port of the BLAKE3 Rust reference implementation

Run test.py to build and test the blake3 binary. The binary hashes stdin and prints the result to stdout. You can run it like this:

$ ./test.py
[build and test output...]
$ echo hello world | ./blake3
dc5a4edb8240b018124052c330270696f96771a63b45250a5c17d3000e823355
$ echo hello world | ./blake3 --len 100
dc5a4edb8240b018124052c330270696f96771a63b45250a5c17d3000e823355675dacfc3ed1a06936ecae2697d6baeaa5e423c0efa51d45b322f3f2ca2ec03d1c5a692d6254d121c20dadf19e0d00e389deb89f2419da878379750df148e9883f482b56
$ echo hello world | ./blake3 --key 0000000000000000000000000000000000000000000000000000000000000000
30f932e14e8cef63f94e658994059fba1a0cf548b01813714c2ce32e2e1c5d3d

Note that putting --key on the command line as in the example above isn't something you should do in production, because other processes on your machine can see your command line arguments. This binary is for demo and testing purposes only and isn't intended for production use.

This implementation tries to be as simple as possible, and the only performance optimization here is liberal use of the inline keyword. Performance isn't terrible though, and under clang -O3 this is a hair faster than Coreutils sha512sum on my laptop.