Exoplanet

++++++++++++++++++

- Updates ``starry`` to get much better performance for high order spherical
harmonics
- Renames ``StarryLightCurve`` to ``LimbDarkLightCurve``
- Restructures the C++ backend to reduce code duplication
- Adds support for fitting of astrometric observations
- Adds support for exposure time integration in ``celerite`` models
- Adds new distributions for periodic parameters and U(0, 1).
- Fixes many small bugs

++++++++++++++++++

- Fixes some edge case failures for Kepler solver
- Improves reliability of contact point solver and fails (more) gracefully
when this doesn't work; this reduces the number of divergences when fitting
a transit model

++++++++++++++++++

- Improves contact point solver using companion matrix to solve quadratic
- Improves reliability of ``Angle`` distribution when the value of the angle
is well constrained

++++++++++++++++++

- Improves the reliability of the PyMC3Sampler
- Adds a new ``optimize`` function since the ``find_MAP`` method
in PyMC3 is deprecated
- Adds cronjob script for automatically updating tutorials.

++++++++++++++++++

- Adds a more robust and faster Kepler solver (`ref
<http://adsabs.harvard.edu/abs/1991CeMDA..51..319N>`_)
- Fixes minor behavioral bugs in PyMC3 sampler wrapper

++++++++++++++++++

- Adds regular grid interpolation Op for Theano
- Fixes major bug in handling of the stellar radius for transits
- Fixes small bugs in packaging and installation
- Fixes handling of diagonal covariances in ``PyMC3Sampler``