Add first go at implementation of K-partial alternatives

Add first go at implementation of K-partial alternatives

The algorithm for computing K-partial alternatives was
added in this commit. It doesn't look super clean
at this point, nor is the code as efficient as it
could be, but it certainly is a first go at an
implementation for K-partial alternatives. Subsequent
commits will attempt to clean up the code and will
implement a version of `Configuration::is_compatible_with()`
which currently remains unimplemented