docs: msgpack-lite is much more efficient for large strings

[D1plo1d]

Just to note, MsgPack-lite is much better then JSON at large strings. If you add a 1.9MB string to the benchmark data you can really start to see an advantage in msgpack-lite's favor. Here's the results I got before the benchmark crashed:

$ ./lib/benchmark.js
operation                                                 |   op   |   ms  |  op/s 
--------------------------------------------------------- | -----: | ----: | -----:
buf = Buffer(JSON.stringify(obj));                        |    100 |  8776 |     11
obj = JSON.parse(buf);                                    |    100 |  6773 |     14
buf = require("msgpack-lite").encode(obj);                |  18000 |  5004 |   3597
obj = require("msgpack-lite").decode(buf);                |  19400 |  5026 |   3859
/home/d1plo1d/git_repos/msgpack-lite/node_modules/msgpack.codec/msgpack.codec.js:204
                Array.prototype.push.apply(rv, mix);
                                     ^

RangeError: Maximum call stack size exceeded

PS. I know 1.9MB is huge, it's a really out there edge case. I am using msgpack-lite to serializing file uploads over WebRTC data channels so for me this is a real world use case and MsgPack totally rocks it!

[D1plo1d]

My results were based on a quick hack at the top of the benchmark:

var data = require("../test/example");
var fs = require("fs");
var longString = fs.readFileSync("/some_directory/benchy.gcode");
data.longString = longString