Mwahpy

- fixed some typos that would prevent the package from initializing correctly
- fixed plot.hist()
- fixed print_particle()
- calc_rvpm() was adding an additional unnecessary (unsupported) key to the
timestep object
- made timestep.recenter() and timestep.update() more verbose
- warnings are now printed, not raised as errors
- typos in plot.fancy_plot()
- fixed incorrect sizing of plot.fancy_plot()

- Now using python's built-in Warning class instead of manually checking flags
and printing warning statements
- orbit_fitter and orbit_fitter_gc now have two modes: 'de' (differential evolution)
and 'gd' (gradient descent). Mode 'de' requires bounds, and mode 'gd' requires
an initial guess. These are selected with the 'mode' keyword in
orbit_fitter.fit_orbit() and orbit_fitter_gc.fit_orbit().
- the phase space coordinates of the Sun are now a PhaseSpace class, which can be
updated throughout the package with mwahpy_glob.solar_ps.update(<[x, y, z, vx, vy, vz]>).
To access the x velocity of the phase space coordinate, for example, you now use
mwahpy_glob.solar_ps.vx.

MAJOR CHANGES:
- now require python v3.6.0 or above due to installation problems with older
versions of python.
- fixed bug in orbit_fitter and orbit_fitter_gc where using numpy arrays for
velocity data would not properly set flags, but lists would crash the program
- progress bars do not show up in jupyter notebooks now, to prevent lagging out
the client
- global flags are now instances of the Flag class (located in flags.py), which
can be switched on or off globally with "myflag.switch(<bool>)". They can still
be treated with default boolean comparisons, e.g. "if myflag:".
MINOR CHANGES:
- phase space of the Sun is now a constant in mwahpy_glob and should be accessed
from there instead of hard-coded
- added fancy_plot() in .plot, can call as timestep.fancy_plot(<...>)
- changed coords.rv_to_vgsr() to coords.vlos_to_vgsr() (trying to avoid overloading
"radial velocity")
- added coords.vgsr_to_vlos()
- didn't need to be importing or utilizing sys
BUG FIXES:
- fixed divide-by-zero error in timestep.get_self_energies()
- fixed bug in coords.rot_around_arb_axis() that was slowing it down slightly
- fixed bug in output_handler.read_output() where the progress bar would not
go from 0 to 100% if the 'stop' keyword was used
- coords.remove_sol_mot_from_pm() no longer modifies the pmra and pmdec input
arrays in place

- renamed orbit_fitting and orbit_fitting_gc to orbit_fitter and orbit_fitter_gc
- refactored and fixed orbit_fitter
- added documentation for orbit_fitter and orbit_fitter_gc
- added documentation for changes since v1.3.5
- functions that were re-used between orbit_fitter and orbit_fitter_gc are now
all located in orbit_fitter
- it's not really a chi-squared, so now it's just a goodness-of-fit in the orbit
fitting packages

- refactored and fixed orbit_fitting_gc
- better way to do coords.cart_to_plane()
- added coords.cart_to_lonlat()
- coords.gal_to_lambet() and coords.cart_to_lambet() now use coords.cart_to_lonlat()
in the background as abstraction
- added coords.gal_to_lambet_galcentric(), will probably be deprecated soon in
order to clarify coordinate systems

- Fixed sign of Ly
- added start and stop keywords to output_handler.read_output()