Lose the boost dependency since recent versions of capnproto's kj
also provide a nice filesystem library. Take the opportunity to
refactor the Run object to become more than POD and to encapsulate
some of the functionality that was done in the Laminar class
Part of #49 refactor
This is a refactor that more cleanly uses the kj framework for handling
processes spawned by Runs. This obviates the workaround introduced back in
ff42dae7cc, and incidentally now requires c++14.
Part of #49 refactor