Created one_grain subdirectory, moved a bunch-o stuff into it.
Altered build process and dependencies to work with new directory structure
Moved discrete_event_handler() into grain_integrator.hpp
Added grian_integrator.cpp and grain_integrator.hpp
Separated grain integration into its own function
Switched back to using odeint as it resulted in faster operation and smoother allocation curves
Added checks so that grains are not run more than once
Moved calendar queue out from inside grains
Isolated calq and GrainEquations into an environment class
Simplified grain_system.cpp and grain_system.hpp
Moved grain_system.cpp and grain_system.hpp to lib/
Updated makefile to appropriately include odeint
Eliminated tubers
Removed tuber
Fixed writing of output