Version 4.0.2
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* Minor changes in the Statistics module: replacing functions 
  resetSamplingCounter and resetTimingCounter with their general analogs.

* Unifying process preemption signals in modules Server and Activity: 
  renaming four signals like that how they are named in the Process module.
  
* The timing statistics (time persistent one) can be normalized to 
  a sampling-based statistics (based upon observation), which allows, 
  for example, building a deviation chart for the queue size.

Version 4.0.1
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* Fixed build issues on GHC 7.10.1.

Version 4.0
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* Added resource preemption.

* Fixed misprint in the activityProcessor function.

Version 3.1
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* Added functions failoverStream and failoverProcessor to model
servers with failures (temporary cancellation of the process with the
further repairing of the server).

* Added functions joinStream and joinProcessor to simplify the
modeling of servers.

* Checking the argument, i.e. time period, in the holdProcess
function. It must not be negative.

* The taskProcess computation behaves exactly like the background
  process, i.e. now its cancellation leads to immediate cancelling the background
  process too.

* Functions setStateActivation, setStateDeactivation and
  setStateTransition are redefined as the Event computations instead
  of Simulation computations.

* Refactored and simplified module Results.