Add some standard methods to Message

This adds `fromString`, `fromJSON`, `toObject`, `toJSON`, `toString`,
and `inspect` to Message. These methods are trivial since Message only
contains a string message, but they should probably be added for
consistency.

Should toBuffer/fromBuffer be added as well?

lib/message.js

@@ -8,6 +8,7 @@ var BufferWriter = bitcore.encoding.BufferWriter;
 var ECDSA = bitcore.crypto.ECDSA;
 var Signature = bitcore.crypto.Signature;
 var sha256sha256 = bitcore.crypto.Hash.sha256sha256;
+var JSUtil = bitcore.util.js;
 
 /**
  * Will construct a new message to sign and verify.
@@ -107,5 +108,61 @@ Message.prototype.verify = function verify(bitcoinAddress, signatureString) {
   return this._verify(publicKey, signature);
 };
 
-module.exports = Message;
+/**
+ * Instantiate a message from a message string
+ *
+ * @param {String} str - A string of the message
+ * @returns {Message} A new instance of a Message
+ */
+Message.fromString = function(str) {
+  return new Message(str);
+};
 
+/**
+ * Instantiate a message from JSON
+ *
+ * @param {String} json - An JSON string or Object with keys: message
+ * @returns {Message} A new instance of a Message
+ */
+Message.fromJSON = function fromJSON(json) {
+  if (JSUtil.isValidJSON(json)) {
+    json = JSON.parse(json);
+  }
+  return new Message(json.message);
+};
+
+/**
+ * @returns {Object} A plain object with the message information
+ */
+Message.prototype.toObject = function toObject() {
+  return {
+    message: this.message
+  };
+};
+
+/**
+ * @returns {String} A JSON representation of the message information
+ */
+Message.prototype.toJSON = function toJSON() {
+  return JSON.stringify(this.toObject());
+};
+
+/**
+ * Will return a the string representation of the message
+ *
+ * @returns {String} Message
+ */
+Message.prototype.toString = function() {
+  return this.message;
+};
+
+/**
+ * Will return a string formatted for the console
+ *
+ * @returns {String} Message
+ */
+Message.prototype.inspect = function() {
+  return '<Message: ' + this.toString() + '>';
+};
+
+module.exports = Message;