Add support for Segwit, BIP49

[i-rme]

Add support for Segwit, for example being able to import BIP49 private keys and generate the corresponding Segwit public address.

[jaonoctus]

+1

[popenkomaksim]

I believe that https://github.com/bip32JP/bip32JP.github.io/tree/master/segwit could be reviewed and reused.

  function generateNewKeyPair(){
      var NETWORK = bitcoin.networks.bitcoin;
      var wif = bitcoin.ECPair.makeRandom({network: NETWORK}).toWIF();
      //var wif = "KyjcD49goTAdFgYj38gnvpwMa1vzaHLoKfJcDFgGr3fikun5DiqL";
      var keyPair = bitcoin.ECPair.fromWIF(wif, NETWORK);
      var pubKey = keyPair.getPublicKeyBuffer();
      var pubKeyHash = bitcoin.crypto.hash160(pubKey);
      var redeemScript = bitcoin.script.witnessPubKeyHash.output.encode(pubKeyHash);
      var redeemScriptHash = bitcoin.crypto.hash160(redeemScript);
      var scriptPubKey = bitcoin.script.scriptHash.output.encode(redeemScriptHash);
      var newaddy = bitcoin.address.fromOutputScript(scriptPubKey, NETWORK);
      return {
          wifPrivateK: wif,
          swAddress: newaddy
      };
  }

Site https://segwitaddress.org/ use this kind of functionality.

[vv01f]

also bech32 encoding of existing keys – needs (compressed) pubkey – would be a fine addition while providing encoding for segwit

[nandubatchu]

@i-rme @jaonoctus @popenkomaksim @vv01f
https://nandubatchu.github.io/bitaddress.org/bitaddress.org.html

@pointbiz Is this PR addressing segwit address format? - #200