Aacgmv2

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* Moved CI support to GitHub actions
* Added a pyproject.toml for PyPi support
* Updated unit tests to current pytest standards
* Updated links in the documentation
* Improved the documentation style and added docstring tests
* Fixed memory leak in the array C wrappers
* Fixed longitude output format for `convert_mlt`
* Added more examples to the documentation

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* Drop support for EOL Python 2.7 and added testing for Python 3.9
* Added a .zenodo.json file
* Fixed AppVeyor environment

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* Moved formerly deprecated utilities from `deprecated.py` to `utils.py`
* Removed allowance for deprecated kwarg `code` from `convert_latlon` and
`convert_latlon_arr`, as scheduled
* Updated CI to include Python 3.8 everywhere
* Moved all configuration information to setup.cfg
* Fixed coveralls implementation
* Fixed broken links in the documentation
* Removed unused code analysis tools
* Improved unit test coverage
* Make PEP8 changes

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* Updated AACGM-v2 coefficients derived using the IGRF13 model
* Updated IGRF and GUFM1 coefficients using the IGRF13 model
* Added additional checks to the C code for reading the IGRF13 coefficient file
* Removed `convert` routine in `deprecated.py`
* Pushed back keyword argument deprecation of `code`
* Scheduled deprecation for remaining routines in `deprecated.py`
* Parametrized several unit tests
* Updated `README.md` examples
* Updated CI to include python 3.8

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* Changed log warning about array functions to info
* Changed default method from `TRACE` to `ALLOWTRACE`
* Added C wrappers for list input, removing inefficient use of `np.vectorize`
* Fixed documentation for use of `method_code`
* Added FutureWarning for deprecated use of `code` keyword argument
* Updated previous version's changelog to encompass all changes
* Improved docstrings to make documentation easier to read
* Removed failing twine commands from `appveyor.yml`
* Removed `RuntimeWarning` filter from `tox.ini`

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* Added FutureWarning to deprecated functions
* Updated names in licenses
* Moved module structure routine tests to their own class
* Added high altitude limit to avoid while-loop hanging
* Changed version support to 2.7, 3.6, and 3.7
* Removed logbook dependency
* Added logic to avoid reseting environment variables if not necessary
* Added copyright and license disclaimer to module-specific program files
* Changed keyword argument `code` to `method_code`