Update README.md
Updated README.md. Replaced errs with err.
Update README.md
Changed signature of callbacks to (errors, results, fl). Use fl.repeatCount rather than 4th param.
Removed flow.tasks(). flow() now returns a function.

..that needs to be called to begin execution. This now allows a flow
task to be added to another flow task.

Also this allows flow task to be called any number of times (because a
new instance of Manager is created everytime).
Send only one argument to first task if error and result isn't passed.
Updated documentation and examples.
Updated README.