Gridopt

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* Compatibility with multiperiod pfnet (dc_opf, nr_pf, augL_pf and augL_opf)

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* Multi-stage stochastic DCOPF.
* Variable generator power curtailment in DCOPF.
* Python 2 and 3 compatibility.

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* Multi-period DCOPF.
* Corrective DCOPF.
* Python 3 and Jupyter compatibility.
* Updated Dockerfile.
* Elastic loads in DCOPF.
* Thermal limits flag in DCOPF.

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* Initial version.