feat: add helpers with common consensus-related code for spending con…

…ditions

lib/consensus/index.js

@@ -0,0 +1,3 @@
+import spendingCondition from './spendingCondition';
+
+export default { spendingCondition };

lib/consensus/spendingCondition.js

@@ -0,0 +1,12 @@
+import { ripemd160, keccak256 } from 'ethereumjs-util';
+
+const getScriptHash = script =>
+  ripemd160(keccak256(script.length), keccak256(script));
+
+const getAddress = script =>
+  `0x${getScriptHash(script).toString('hex')}`;
+
+export default {
+  getScriptHash,
+  getAddress,
+};

lib/index.js

@@ -20,3 +20,5 @@ export { default as Output } from './output';
 export { default as Outpoint } from './outpoint';
 export { default as Util } from './util';
 export { default as Exit } from './exit';
+
+export { default as Consensus } from './consensus/';