Calliope

* Fixes to time_functions
* Other minor improvements and fixes

* Python 3 and Pyomo 4 are now minimum requirements
* Significantly improved documentation
* Improved model solution management by saving to HDF5 instead of CSV
* Calculate shares of technologies, including the ability to define groups for the purpose of computing shares
* Improved operational mode
* Simplified time_tools
* Improved output plotting, including dispatch, transmission flows, and installed capacities, and added model configuration to support these plots
* ``r`` can be specified as power or energy
* Improved solution speed
* Better error messages and basic logging
* Better sanity checking and error messages for common mistakes
* Basic distance-dependent constraints (only implemented for e_loss and cost of e_cap for now)
* Other improvements and fixes

* Added cost classes with a new set ``k``
* Added energy carriers with a new set ``c``
* Added conversion technologies
* Speed improvements and simplifications
* Ability to arbitrarily nest model configuration files with ``import`` statements
* Added additional constraints
* Improved configuration handling
* Ability to define timestep options in run configuration
* Cleared up terminology (nodes vs locations)
* Improved TimeSummarizer masking and added new masks
* Removed technology classes
* Improved operational mode with results output matching planning mode and dynamic updating of parameters in model instance
* Working parallel_tools
* Improved documentation
* Apache 2.0 licensed
* Other improvements and fixes

* Some semblance of documentation
* Usable built-in example model
* Improved and working TimeSummarizer
* More flexible masking for TimeSummarizer
* Ability to add additional constraints without editing core source code
* Some basic test coverage
* Working parallel run configuration system