Describe the problem you'd like to have solved

Add the ability to execute requests asynchronously.

Describe the ideal solution

See #112 for a possible solution to add async support. Note that to avoid a breaking change by adding a new method to the Request interface, we could consider adding a new default method for async execution (would probably just have to throw an UnsupportedOpertationException).

Additional information, if any

This is dependent on #314 being completed first.