Pdspy

A major upgrade to pdspy, which is not backwards compatible to versions < 2.0.0. Updates include:

- x0, y0 now defined in the proper sense as opposed to backwards as they were before
- Position angles reported are now defined correctly, so no post-processing needed
- Supply the code directly with CASA MS files (requires Python 3.6 and CASA6)
- Fourier Transforms of model images are now done entirely with either GALARIO or TriFT, and an option to choose between them exists.

Drop the evolutionary tracks as part of the package as they were making the package too large.

Fixes pdspy.radmc3d.run.sed to match the new format from RADMC3D where "spectrum" is used to generate SED's at user defined wavelengths for the v1 version of pdspy.

A new release built on top of v1.5.3 to add the ability to adjust the mean molecular weight when using flared_model. This feature coming to v2.* soon!

Further updates to v1.5, including:

* Better estimate of the CLEAN beam shape in uv.clean
* New routine to plot PV diagrams of the results of model fits
* Use KDE to find peaks in the posteriors of model fits.
* A number of minor bug fixes

Some minor updates to v1.5, including:

- Adding a tool to load results of fits under the hood, with a number of options
- Ability to adjust weighting of images in plot_channel_maps
- Fully working readms function