Experimental support for synchronous tasks

[vasilev]

It's experimental support for tasks which acted as synchronous.

Usage example:

task := worker.Task{CodeName: "iron/hello"}
w := worker.New()
result, err := w.TaskRun(task)

result will contain a task's stdout.

[rkononov]

@vasilev need to update readme

[vasilev]

@rkononov Added an example and updated the README .