Use parse-torrent by feross

There's no point on implementing multiple versions of a torrent parser.
Let's use feross' and maintain only one. His version is based on this project's original algorithm, but he improved it to make it work in browsers too, which is fine, and removed a few dependencies.

Commit changes:

- Parse with `parse-torrent`
- Ensure a true asynchronous callback with `process.nextTick`
- Updated README.
- Added error checking in cli.js