[WIP] Update documentation to reflect API changes

[dylanagreen]

The documentation for fiberassign, most notably the "usage" page that defines a minimal example of how the package should be used and run, refer to API elements that are significantly out of date. In some cases the example refers to scripts that don't exist anymore or have been renamed. This PR aims to update these instances where noted to bring the documentation inline with the most recent version of fiberassign. Major changes documented here:

fba_run

The command line arguments of fba_run have changed significantly since the last documentation update. Notably the following two arguments have been removed:

• --positioners
• --status

The following arguments were added:

• --ha
• --fieldrot
• --fieldrot_corr
• --sky_per_slitblock
• --margin-pos
• --margin-petal
• --margin-gfa
• --gaia_stdmask
• --by-tile
• --no-redistribute
• --lookup_sky_source
• --fafns_for_stucksky
• --fba_use_fabs

fba_plot

fba_plot_results was at some point renamed fba_plot, but this was not documented in the documentation. All instaces of fba_plot_results have been updated to now correctly refer to fba_plot. Usage of the script has also changed, instead of giving it a file of tiles to plot fba_plot reads everything necessary from the associated fiber assignment file produced by fba_run. The Usage page has been updated to reflect this fact.

This PR is still a WIP, additional documentation updates are expected in the near future.