Add taskify

[dggluz]

Decription

I'm not totally sure about how should be this function be to avoid being too specific to certain API, but it would be handy to avoid having to always do:

new Task((resolve, reject) => {
    funcTooBeTaskified(resolve, opts, reject);
});

[dggluz]

It should probably be another version (or make this version flexible enough to support it) for the functions that throw errors instead of passing it as parameters via CPS.

Two examples that illustrate both forms are: fs.readFile and JSON.parse.