Added

Added plot and particle_plot as methods of the Snap class. This allows for plotting with snap.plot(quantity='quantity') as opposed to plonk.visualize.plot(snap=snap, quantity='quantity).
Axis and colorbars have labels by default now, including units.
The to_dataframe Snap method now indicates units in the column names, e.g. position [au].
The available_arrays method of Snap has additional arguments to see all sub-arrays on particles, e.g. velocity_x and dust_fraction_001.
Added to examples and quick-start in documentation.
Added method to re-open a closed Snap file.

Changed

Physical units are turned on by default on Snap objects. All particle and sink arrays have units (provided by Pint).
The units attribute of Snap and Simulation now only has core units, i.e. length, time, mass, and magnetic field.
Some extra quantities have been renamed.
Extra quantities are available on Snap objects by default.
The arguments radius_min and radius_max in Profile have been renamed cmin and cmax to reflect that profiles are not just radial.