Eemeter

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* Update observed_mean calculation to account for solar (negative usage) to provide
sensible cvrmse calculations.

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* Remove missing hour_of_week categories in the CalTrack hourly methods so they predict null for those hours.

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* Remove python27 support.
* Update Pipfile lock.
* Update `fit_temperature_bins` to potentially take an `occupancy_lookup` in order to
fit different temperature bins for occupied/unoccupied modes. *This changes the args passed to eemeter.create_caltrack_hourly_segmented_design_matrices, where it now requires a set of bins for occupied and unoccupied temperatures separately.*
* Update CalTRACK hourly model formula to use different bins for occupied and
unoccupied mode.

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* Fix tests and make changes to ensure tests pass on pandas version 1.2.1.
* Fix bug in segmentation.py causing a section of tutorial to fail.

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* Add additional terms into ModelMetrics() class which can be used in fractional savings uncertainy computations.

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* Remove fixing of versions of libraries in setup.py to avoid unforeseen issues with library updates.