add migrations

migrations/002-bills.js

@@ -0,0 +1,20 @@
+'use strict';
+
+var db = require('./db');
+
+exports.up = function(next){
+  db.query('CREATE TABLE bills ( ' +
+    'id uuid PRIMARY KEY, ' +
+    'device_fingerprint text NOT NULL, ' +
+    'denomination integer NOT NULL, ' +
+    'currency_code text NOT NULL, ' +
+    'satoshis integer NOT NULL, ' +
+    'to_address text NOT NULL, ' +
+    'session_id uuid NOT NULL, ' +
+    'device_time bigint NOT NULL, ' +
+    'created timestamp NOT NULL DEFAULT now() )', next);
+};
+
+exports.down = function(next){
+  next();
+};