Review synchronize.js

[ricardojmendez]

Review synchronize.js, consider migrating to it from fibers.

Suggested by @yogthos.

[ricardojmendez]

I've ben reviewing this and discussing it with @yogthos. In short:

• We're not really migrating from fibers, as synchronize.js is built on them;
• I don't really see yet what the synchronize approach buys us over futures, as far as actual use goes

We'll still need to make a synchronous wrapper for the async function, which will likely have the same drawbacks when wrapping instance methods. We'll still need to have some function grouping together the calls we want to make synchronous (whether it is a task or just a fiber). We just add a slightly different approach which could be lighter than futures, but also introduces more code (since futures are already bundled with the base fibers package).