Support part buffer for decode

[KlonD90]

It's about that works in this way:

var b = Buffer.alloc(1000);
msgPackBuffer.copy(b, 100);
var obj = m.decode(b, {from: 100, length: msgPackBuffer.length});

My case: https://github.com/KlonD90/node-tarantool-driver. Now work for optimisation and use your implementation. I want less allocation for more speed/less memory usage.

Please help me with improve this. Can i pull request you or do something for this way?

[kawanet]

There is a public but undocumented lower-level class Decoder as I've mentioned at #31. I guess the code below would work with this class.

var Decoder = require("msgpack-lite").Decoder;
var decoder = new Decoder();
decoder.buffer = msgPackBuffer;
decoder.offset = 100;
var obj = decoder.fetch(); // decode the first element only

[KlonD90]

@kawanet thank you :) it is very helpful for me.