Pmpy

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- [Added] Ability to cancel requests for resoruces. this allows modeling or between resource requests

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- [Fixed] fixed namings of logs.

- [Added] added waiting time for resources.

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- [Fixed] Fixed numbering of entities in the discrete event simulation environment.

- [Fixed] Fixed spelling of preemptive resources.

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- [Fixed] fixed splelling of environment class.

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- [NEW] Added Docstrings for discrete event simulation.

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- [CHANGE] Updated PmPy package structure. PmPy now has a `simulation` subpackage that includes `discrete_event` and `distributions` modules.