Sncosmo

===================

- Add ZTF transmission functions

- Bugfixes

- Corrected pyproject.toml; should help cases where the wrong numpy
version was being installed.

- Remove all references to the six package

- Fix accidental mutation of ``bounds`` inputs in ``fit_lc`` and
``mcmc_lc``.

===================

This version is the same as v1.8, with the exception that Python 2 support
has been removed, and deprecated functions and attributes have been removed.
These were deprecated in v1.5.0 (released April 2017) or before.

On Python 2, pip should automatically install sncosmo v1.8 still. If not,
specify ``sncosmo<2.0.0``.

Minor changes:

- The ``salt2-h17`` source model has been renamed to ``salt2-extended-h17``
to make clearer its relation to ``salt2-extended``. It is still available
under the old name for backwards compatibility.

===================

- Fix bug in download location of ``snana-*`` models latest versions,
introduced in v1.8.0.

===================

- Fix bug in download location of ``salt2-extended`` model latest version,
introduced in v1.8.0.

===================

- Add version 2.0 of many ``snana-...`` built-in core-collapse models,
based on Pierel et al. 2018 (pull request 229).

- Bugfixes:

- Fix compatibility with scipy 1.3+ by removing outdated import statements
(pull request 238).

- Fix issue affecting optimization of models with free propagation effects
(pull request 236).

===================

- Add SNEMO2, SNEMO7, SNEMO15 source models from Saunders et al. (2018)
to built-ins.