allow bufferreader.read to specify length

...to be more symmetric with the write function of bufferwriter

lib/bufferreader.js

@@ -28,7 +28,9 @@ BufferReader.prototype.buffer = function(len) {
   return buf;
 };
 
-BufferReader.prototype.read = function() {
+BufferReader.prototype.read = function(len) {
+  if (len)
+    return this.buffer(len);
   var buf = this.buf.slice(this.pos);
   this.pos = this.buf.length;
   return buf;

test/bufferreader.js

@@ -58,6 +58,16 @@ describe('BufferReader', function() {
       br.read().toString('hex').should.equal(buf.toString('hex'));
     });
 
+    it('should return a buffer of this length', function() {
+      var buf = new Buffer(10);
+      buf.fill(0);
+      var br = new BufferReader(buf);
+      var buf2 = br.read(2);
+      buf2.length.should.equal(2);
+      br.eof().should.equal(false);
+      br.pos.should.equal(2);
+    });
+
   });
 
   describe('#readUInt8', function() {