Phoebe

* removes m2r as an (unlisted) build-dependency. m2r is only required to build the submission to submit to pypi, but is not required to install or run phoebe locally.

* Add support for inverse problem solvers, including "estimators", "optimizers", and "samplers"
* Add support for attaching distributions (as [distl](https://github.com/kecnry/distl) objects) to parameters, including priors and posteriors.
* Add support for [web and desktop clients](http://phoebe-project.org/clients) via a light-weight built in `phoebe-server`.
* Removed support for Python 2 (now requires Python 3.6+)
* Implement optional gaussian processes for light curves
* Implement phase-masking
* Added official support for [ellc](https://github.com/pmaxted/ellc) and [jktebop](https://www.astro.keele.ac.uk/jkt/codes/jktebop.html) alternate backends
* Per-component and per-dataset RV offsets
* Fixed phasing in time-dependent systems
* Distinction between anomalous and sidereal period in apsidal motion cases
* Extinction parameters moved from per-dataset to the system-level
* Added several new optional constraints
* Overhaul of the run_checks framework
* Updated scipy dependency to 1.7+
* Numerous small bugfixes and enhancements

* fix overriding mesh_init_phi as kwarg to run_compute
* fix pblum computation to not require irrad_method kwarg
* fix bundle representation to exclude hidden parameters

* Improves the detection of g++/gcc version to compare against requirements during setup.

* Add support for interstellar extinction/reddening.
* Support for Python 3.6+ in addition to Python 2.7+.
* Overhaul of limb-darkening with new ld_mode and ld_coeffs_source parameters.
* Overhaul of passband luminosity and flux scaling with new pblum_mode parameter, including support for maintaining color relations between multiple passbands.
* Ability to provide third light in either flux or percentage units, via the new l3_mode and l3_frac parameters.
* Support for computing a model at different times than the observations, via the new compute_times or computes_phases parameter.
* Transition from pickled to FITS passband files, with automatic detection for available updates. The tables can now also be accessed via tables.phoebe-project.org.
* DISABLED support for beaming/boosting.
* Allow flipping Kepler's thrid law constraint to solve for q.
* Require overwrite=True during add_* or run_* methods that would result in overwriting an existing label.
* Constraint for logg.
* Account for time-dependence (dpdt/dperdt) in t0 constraints.

* Future-proof to ignore for passband files with extensions other than ".pb" which may be introduced in future versions of PHOEBE.