[FEATURE] Provide asynchronous process execution API

[dbwiddis]

Is your feature request related to a problem?

In #17, a process sequence with predecessor requirements will be generated. Use this sequence to actually execute process steps when predecessors are complete.

What solution would you like?

An execution of the process will complete the following steps:

1. Iterate through the entire sequence, calling a method that returns a completable future immediately.
2. The method will take a collection of predecessor step completable futures (generated in step 1) as an argument, and delay further execution until an an allOf() completable future is complete.
3. When the step is actually complete, complete the future, which will be used by a future step.

Do you have any additional context?

This is the same type of execution currently used in plugins to execute a sequence of events. It just needs to be adapted to rely on multiple predecessor steps.