Parallel/Serial Runner options

[ghthor]

This is the execution of the idea I expressed in #6.

• TODO Specs - This is a quick hack, to get work done. Spec'ing this is on mine and rafrombrc's todo list.

TL:DR;

type Runner interface {
...
}  

type SerialRunner struct {
...
}  

type ParallelRunner struct {
...
}