Refactor solver module

[mattjones315]

Per a recent conversation in issue #205, we've determined that our recent software development efforts have outstripped the implementation of the DistanceSolver class. Namely, it's become apparent that the inheritance structure is limiting our ability to cleanly implement new distance-based algorithms and perhaps makes things unneccessarily complex. A move to composition-based software has been proposed.

The purpose of this issue is to discuss & plan a refactor of the DistanceSolver class and perhaps the entire solver module. In doing so, it would be ideal to maintain the current API as much as possible as to not break any existing code already relying on the solver module.