Sometimes upstreams can accept HTTP but never respond causing requests
to build up waiting for a response. This can block Process.Stop() as
that waits for inflight requests to finish. This change refactors the
code to not wait when attempting to shutdown the process.
Groups allows more control over swapping behaviour when a model is requested. The new groups feature provides three ways to control swapping: within the group, swapping out other groups or keep the models in the group loaded persistently (never swapped out).
Closes#96, #99 and #106.