Improve memory usage

[dukex]

I'm working on https://github.com/databr/datasus/tree/databr, and I find a way to improve memory usage:

• use https://github.com/cheeriojs/cheerio instead of jsdom
  You will need change things like:

var div = html_document.find("div[style='width:539; height:500; POSITION: absolute; TOP:198px; LEFT: 121px; overflow:auto']");
var table = html_document(div).find("table");
var links = html_document(div).find("a");

to

var div = html_document.find("div[style='width:539; height:500; POSITION: absolute; TOP:198px; LEFT: 121px; overflow:auto']");
var table = div.find("table");
var links = div.find("a");

and trs[i] .... to trs.eq(i) ...

• Create a request pool with https://github.com/coopernurse/node-pool

Soon I push some changes to my branch