add address validation convenience function

lib/address.js

@@ -10,6 +10,12 @@ function Address(obj) {
     this.set(obj);
 };
 
+Address.validate = function(addrstr) {
+  var address = new Address().fromString(addrstr);
+  address.validate();
+  return this;
+};
+
 Address.prototype.set = function(obj) {
   this.hashbuf = obj.hashbuf || this.hashbuf || null;
   this.networkstr = obj.networkstr || this.networkstr || 'mainnet';

test/test.address.js

@@ -12,6 +12,14 @@ describe('Address', function() {
     should.exist(address);
   });
 
+  describe('@validate', function() {
+
+    it('should validate this valid address string', function() {
+      should.exist(Address.validate(str))
+    });
+
+  });
+
   describe('#fromPubkey', function() {
 
     it('should make this address from a compressed pubkey', function() {