examples: add tx example.

examples/tx.js

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+'use strict';
+
+var bcoin = require('bcoin');
+var assert = require('assert');
+
+var master = bcoin.hd.generate();
+var key = master.derive('m/44/0/0/0/0');
+var keyring = new bcoin.keyring(key.privateKey);
+var cb = new bcoin.mtx();
+
+cb.addInput({
+  prevout: new bcoin.outpoint(),
+  script: new bcoin.script(),
+  sequence: 0xffffffff
+});
+
+// Send 50,000 satoshis to ourselves.
+cb.addOutput({
+  address: keyring.getAddress(),
+  value: 50000
+});
+
+// Our available coins.
+var coins = [];
+
+// Convert the coinbase output to a Coin
+// object and add it to our available coins.
+// In reality you might get these coins from a wallet.
+var coin = bcoin.coin.fromTX(cb, 0, -1);
+coins.push(coin);
+
+// Create our redeeming transaction.
+var mtx = new bcoin.mtx();
+
+// Send 10,000 satoshis to ourself.
+mtx.addOutput({
+  address: keyring.getAddress(),
+  value: 10000
+});
+
+// Now that we've created the output, we can do some coin selection (the output
+// must be added first so we know how much money is needed and also so we can
+// accurately estimate the size for fee calculation).
+
+// Select coins from our array and add inputs.
+// Calculate fee and add a change output.
+mtx.fund(coins, {
+  // Use a rate of 10,000 satoshis per kb.
+  // With the `fullnode` object, you can
+  // use the fee estimator for this instead
+  // of blindly guessing.
+  rate: 10000,
+  // Send the change back to ourselves.
+  changeAddress: keyring.getAddress()
+}).then(function() {
+  // Sign input 0
+  mtx.sign(keyring);
+
+  // The transaction should now verify.
+  assert(mtx.verify());
+
+  // Commit our transaction and make it immutable.
+  // This turns it from an MTX into a TX.
+  var tx = mtx.toTX();
+
+  // The transaction should still verify.
+  // Regular transactions require a coin
+  // viewpoint to be passed in.
+  assert(tx.verify(mtx.view));
+
+  console.log(mtx);
+});