Chaosmagpy

Features
^^^^^^^^
* :func:`chaosmagpy.data_utils.mjd_to_dyear` and
:func:`chaosmagpy.data_utils.dyear_to_mjd` convert time with microseconds
precision to prevent round-off errors in seconds.
* Time conversion now uses built-in ``calendar`` module to identify leap year.

Bugfixes
^^^^^^^^
* Fixed wrong package requirement that caused the installation of
ChaosMagPy v0.1a1 to fail with ``pip``. If installation of v0.1a1 is needed,
use ``pip install --no-deps chaosmagpy==0.1a1`` to ignore faulty
requirements.

Features
^^^^^^^^
* Package now supports Matplotlib v3 and Cartopy v0.17.
* Loading shc-file now converts decimal year to ``mjd2000`` taking leap years
into account by default.
* Moved ``mjd2000`` from ``coordinate_utils`` to ``data_utils``.
* Added function to compute degree correlation.
* Added functions to compute and plot the power spectrum.
* Added flexibility to the function synth_values: now supports NumPy
broadcasting rules.
* Fixed CHAOS class method synth_coeffs_sm default source parameter: now
defaults to ``'external'``.

Deprecations
^^^^^^^^^^^^
* Optional argument ``source`` when saving shc-file has been renamed to
``model``.
* ``plot_external_map`` has been renamed to ``plot_maps_external``
* ``synth_sm_field`` has been renamed to ``synth_coeffs_sm``
* ``synth_gsm_field`` has been renamed to ``synth_coeffs_gsm``
* ``plot_static_map`` has been renamed to ``plot_maps_static``
* ``synth_static_field`` has been renamed to ``synth_coeffs_static``
* ``plot_tdep_maps`` has been renamed to ``plot_maps_tdep``
* ``synth_tdep_field`` has been renamed to ``synth_coeffs_tdep``

Initial release to the users for testing.