Add Currency formatter

* src/validate/formatter/Currency.js: Add class.

src/validate/formatter/Currency.js

@@ -0,0 +1,36 @@
+/**
+ * @license
+ * Currency formatter
+ *
+ *  Copyright (C) 2016 LoVullo Associates, Inc.
+ *
+ *  This file is part of liza.
+ *
+ *  liza is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/**
+ * Currency of the form `$%2.f`
+ *
+ * @example
+ *   Currency().parse( '$123' );      // => 123.00
+ *   Currency().retrieve( '123.4' );  // => $123.40
+ *
+ * @class Currency
+ * @mixes module:validate/formatter.Number
+ * @mixes module:validate/formatter.StringFormat
+ */
+module.exports = require( './EchoFormatter' )
+    .use( require( './Number' )( 2 ) )
+    .use( require( './StringFormat' )( '$%s' ) );