Implement ScriptableBuffer

As mentioned in email, it provides basic functionalities to manipulate buffers with String and Byte. For the class methods, Node.js [Buffer](http://nodejs.org/api/buffer.html) is referred to. Following methods are implemented.

* `new Buffer(size)`
* `new Buffer(array)`
* `new Buffer(str, [encoding])`
* `Class Method: Buffer.isEncoding(encoding)`
* `buf.write(string, [offset], [length], [encoding])`
* `buf.toString([encoding], [start], [end])`
* `buf.toJSON()`
* `buf[index]`
* `Class Method: Buffer.byteLength(string, [encoding])`
* `Class Method: Buffer.concat(list, [totalLength])`
* `buf.length`
* `buf.copyTo(targetBuffer, [targetStart], [sourceStart], [sourceEnd])`
* `buf.slice([start], [end])`
* `buf.fill(value, [offset], [end])`