Ligo.skymap

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

- Fix a bug in ``ligo-skymap-plot-airmass`` that caused the airmass chart to be
blank if the lower and upper credible levels were always in opposite
hemispheres. The root cause was that ``plt.fill_between`` does not clip
infinities to the plot's data range.

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

- Require lalsuite >6.53 and lscsoft-glue >=2.0.0 due to breaking changes in
API and behavior for LIGO-LW XML reading.

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

- Pin lalsuite at <=6.52 and lscsoft-glue at <=1.60.0 due to breaking changes
in API and behavior for LIGO-LW XML reading.

- Add the ``ligo-skymap-unflatten`` tool to convert flat, fixed resolution,
implicitly indexed HEALPix files to multi-resolution HEALPix files. This
tools is the inverse of ``ligo-skymap-flatten``.

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

- Migrate from glue.segments to ligo.segments.

- Add ``--min-inclination`` and ``max-inclination`` options to
``bayestar-localize-coincs`` and ``bayestar-localize-lvalert`` to control the
limits of the isotropic prior over the inclination angle.

- Un-pin ligo-segments and require version >= 1.2.0 due to packaging
bugfixes.

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

- Fix a bug that prevented the output of ligo-skymap-flatten from being
gzip-compressed if the output filename ended in .gz.

- Require astropy >= 3.1 because some code that we previously had to
monkeypatch went upstream. See
https://github.com/astropy/astropy-healpix/pull/106.

- In the KDE clustering and ``ligo-skymap-from-samples``, disable OpenMP
parallelism if Python mulitprocessing parallelism is enabled. This will
prevent the program from spawning an excessive number of threads.

- ``ligo-skymap-plot`` no longer requires a DATE-OBS entry in the FITS header
when plotting in astronomical coordinates.

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

- Fix a typo that caused ligo.skymap to always compile the bundled copy of
chealpix instead of searching for a system version using pkgconfig.

- Un-pin Numpy version now that Numpy 1.15.4 is out.

- The ``bayestar-localize-lvalert`` and ``ligo-skymap-from-samples`` tools can
now natively output multi-resolution HEALPix files, although they still
natively output flat, fixed-resolution HEALPix files.

- Add the ``ligo-skymap-flatten`` tool to convert multi-resolution HEALPix
files to flat, fixed-resolution, implicitly indexed HEALPix files.

- Bring back ``bayestar_samples_ppplot`` from LALInference as
``ligo-skymap-plot-pp-samples``, a tool for making P-P plots to compare a sky
map with posterior samples.

- Add ``--cosmology`` feature to ``ligo-skymap-stats`` to calculate comoving
volumes.