no_std support

[mcroad]

Hello,

I'm attemting to build the library for an embedded environment. Are there plans to support no_std as a target?

rust-bitcoin and rand already support no_std. rust-crypto is the only dependency that does not support no_std. rust-crypto's last commit is in 2016. It seems like it's not in active development anymore. However, in DaGenix/rust-crypto#405 someone mentions @RustCrypto as a successor. The RustCrypto crates are still in active development and have no_std support

From looking at the code, I gather these are the encryption algorithms used. RustCrypto has an implementation for all of them.

rust-crypto	RustCrypto	no_std	Repo
HMAC	✔️	✔️	https://github.com/RustCrypto/MACs
SHA256	✔️	✔️	https://github.com/RustCrypto/hashes/
SHA512	✔️	✔️	https://github.com/RustCrypto/hashes/
PBKDF2	✔️	✔️	https://github.com/RustCrypto/password-hashes/
AES	✔️	✔️	https://github.com/RustCrypto/block-ciphers

Is this something the @rust-bitcoin team would be interested in? If so, I could submit multiple pr's slowly replacing rust-crypto with the @RustCrypto crates.

[mcroad]

Closing in favor of bitcoindevkit/bdk#205