now supports methods-calling-methods

Introduces a "parent" information.

When we add a task and a parent has not yet finished, then we auto
advance to the child.

We can auto advance since the parent `callback` will be called by one of
his childs to complete the chain.
0.0.2
add failling test using setTimeouts

refactor, handle a lot more async/nextTick/nested chains cases

Turns ou I needed to handle one queue per chain depth
precise readme
0.0.3
show off
Merge pull request #1 from vvo/beta

Full refactor, handle a lot more cases and async traps