Add Examples

[Sosthene00]

Create a examples dir to help people figure out how to use the lib.

[vincenzopalazzo]

ACK c594ddd

Thanks! :)

[cygnet3]

Receiving part looks good. Maybe we can also show some examples with hardcoded values?
For example, this worked for me:

cargo run --example find_output "sock wait angry photo endless ready dune mechanic ketchup crowd inhale cat" "020000000001012c8a11d71cf530e68fda5e408dbbafb021e7451568e7bbfea286fc76ac0cd5680000000000fdffffff018012000000000000225120ccbebdd796de2333747d5fa88109abcb463d92548a7dbc68e9cf68bd7c1d206202463043021f0a8c1628e5c50402016627ec1789a862d344cbb49d7e34f99551b5020ce73d02205190ed8c8eda534b719bb0117309cea1f5f3a6b0fc76693a996d140f75ab4e0d012103529dbe46ef50b96fdb89925631156ea31296cef4ba4b2e0b4ba4799ba4499e6240dc0200" "001471c944097ff1f456df4efc8723a508af1d5c7c7f"

[cygnet3]

Maybe we can also print the descriptor with the checksum? To import it with bitcoin core you need the checksum iirc. This is how I do it:

    let rawtr = format!("rawtr({})", privkey.to_wif());
    let checksum = bdk::descriptor::checksum::calc_checksum(&rawtr).unwrap();

    println!("descriptor: {}#{}", rawtr, checksum);

though this also adds bdk as a dependency.

[cygnet3]

As for sending, a very simple example would be:

    // address to send to
    let sp_address = "tsp1q...".to_string();

    // get the xprv from a given seed phrase
    let mnemonic = Mnemonic::from_str("...").unwrap();
    let root_xprv = Xpriv::new_master(Network::Signet, &mnemonic.to_seed("")).unwrap();

    // get single key from some derivation path, this is the only input we use
    let derivation_path: DerivationPath = DerivationPath::from_str("m/84'/1'/0'/0/0").unwrap();
    let sender_key = root_xprv
        .derive_priv(&secp, &derivation_path)
        .unwrap()
        .to_priv()
        .inner;

    // get the prevout for this private key, from a utxo that 'belongs' to this private key
    let txid = "...";
    let vout = 0;

    let input_keys = [(sender_key, false)];
    let outpoints_data = [(txid.to_owned(), vout)];
    let partial_secret = calculate_partial_secret(&input_keys, &outpoints_data).unwrap();
    let mut output = generate_recipient_pubkeys(vec![sp_address], partial_secret).unwrap();
    let output = output.remove(&sp_address).unwrap()[0];

    let assumetweaked = TweakedPublicKey::dangerous_assume_tweaked(output);
    let p2tr_address = Address::p2tr_tweaked(assumetweaked, Network::Signet);
    println!("p2tr address: {:?}", p2tr_address);

but then get these argument from command line args.
Of course, that might be too simple/not very accurate for wallet developers.