more convenient constructor

...allow inputing strings or buffers in the constructor.

lib/base58check.js

@@ -4,8 +4,15 @@ var sha256sha256 = require('./hash').sha256sha256;
 var Base58Check = function Base58Check(obj) {
   if (!(this instanceof Base58Check))
     return new Base58Check(obj);
-  if (obj)
+  if (Buffer.isBuffer(obj)) {
+    var buf = obj;
+    this.fromBuffer(buf);
+  } else if (typeof obj === 'string') {
+    var str = obj;
+    this.fromString(str);
+  } else if (obj) {
     this.set(obj);
+  }
 };
 
 Base58Check.prototype.set = function(obj) {

test/base58check.js

@@ -16,6 +16,11 @@ describe('Base58Check', function() {
     should.exist(b58);
   });
 
+  it('should allow this handy syntax', function() {
+    Base58Check(buf).toString().should.equal(enc);
+    Base58Check(enc).toBuffer().toString('hex').should.equal(buf.toString('hex'));
+  });
+
   describe('#set', function() {
     
     it('should set a buf', function() {