2732891359 Change rand to rand-std in lib.rs documentation (Vincent Liao)
Pull request description:
I copy-pasted the key-generation example written on the documentation, but it didn't work. It only worked when I used the feature `rand-std` instead of `rand`.
To reproduce, boot up a new Rust project, and add this to main.rs:
```
use secp256k1::rand::rngs::OsRng;
use secp256k1::{Secp256k1, Message};
use secp256k1::hashes::sha256;
let secp = Secp256k1::new();
let mut rng = OsRng::new().expect("OsRng");
let (secret_key, public_key) = secp.generate_keypair(&mut rng);
let message = Message::from_hashed_data::<sha256::Hash>("Hello World!".as_bytes());
let sig = secp.sign_ecdsa(&message, &secret_key);
assert!(secp.verify_ecdsa(&message, &sig, &public_key).is_ok());
```
Using this dependencies causes error: `secp256k1 = {version="0.21.2", features=["rand", "bitcoin_hashes"]}`. After replacing `rand` with `rand-std`, it works.
ACKs for top commit:
apoelstra:
ACK 2732891
tcharding:
tACK 2732891359
Tree-SHA512: 6b5436bc71bab7535e432e119679bc6bcb11d2575b609e039cc25c122ae92b528f95a673e9c643a6cfa2ee3a663f7efdd61731b6084261c52a220448b6f72d12
7a3736a0f9