Minor fix.
Some reworks to ease future transition to ES6 generators.

It will also helped to achieve more parallelism.
Unit tests for fiber utils.
Minor nesting bug.
Minor changes.
Preparation work to have a promise-based XAPI connection.
Badges added to the README to see if dependencies are up to date (fix #21).
Updates all dependencies.
Uses `npm shrinkwrap` to fix dependencies' versions (fix #22).
Bumps version number.
Merge branch 'next-release'