This change updates the project structure to become flattened.
Previously, the simulator, frontend and API each lived into their own
directory.

With this change, all modules of the project live in the top-level
directory of the repository. This should improve discoverability of
modules of the project.

This change adds a power model for optimizing the mean squared error 
to the available power models in OpenDC.

This change fixes and issue where a SimWorkload was being re-used across
simulation runs. Given that SimWorkload is stateless, this may cause
strange issues.

This change introduces the SimProcessingUnit which represents a
simulated processing unit which the user can control during the workload
execution.

This change adds the asymptotic power model that is used in GreenCloud
to the available power models in OpenDC.

This change adds an experiment for the OpenDC Energy project, which
tests various energy models that have been implemented in OpenDC.

This change fixes an issue in SimTraceWorkload where the CPU usage was
not divided across the cores, but was instead requested for all cores.

This change updates the logic in SimAbstractMachine to only propagate
usages when the value has changed.

This change removes the StateFlow speed property on the
SimResourceSource, as the overhead of emitting changes to the StateFlow
is too high in a single-thread context. Our new approach is to use
direct callbacks and counters.