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 model implementing Dynamic Voltage Frequency Scaling
(DVFS) to OpenDC.

This change moves the power models from the `opendc-compute-simulator`
to the `opendc-simulator-compute` module, since it better fits the scope
of the models and allows them to be re-used for other purposes.

This change removes the generic resource constraint (e.g., SimResource)
and replaces it by a simple capacity property. In the future, users
should handle the resource properties on a higher level.

This change simplifies compositions of consumers and providers by not
requiring a translation from resource to capacity.

This change adds support for aggregating code coverage results from the
different modules.

This change adds a generic framework for modeling resource consumptions and
adapts opendc-simulator-compute to model machines and VMs on top of
this framework.

This framework anticipates the addition of additional resource types
such as memory, disk and network to the OpenDC codebase.

This change removes the opendc-core module. This module was an artifact
of the old codebase and remained mostly unused. This change removes all
usages of the module and if necessary introduces replacement classes.

This change removes the usage of bare-metal provisioning from the OpenDC
Compute module. This significantly simplifies the experiment setup.