Dbsp-drp

What's new:

- dbsp_splice script to allow users to manually splice two coadded files together.
- archived sensitivity functions for setups blue_300_3990_d55, blue_600_4000_d68 red_600_10000_d55 red_1200_7100_d68 red_1200_9400_d55
- dbsp_trim script to trim a spliced spectrum to a final wavelength range of interest
- uses PypeIt version 1.6.0
- improved documentation
- added Community Guidelines
- many bug fixes and improved stability

**Full Changelog**: https://github.com/finagle29/DBSP_DRP/compare/v0.9.0...v1.0.0

DBSP_DRP version 0.9.0 is close to a stable, v1.0-ready product. However, the only instrument configuration supported in this release is 600/4000 on the blue side, 316/7500 on the red side, and the D55 dichroic. Future releases will expand instrument configuration support. Also, the red side CCD artifact that appeared in May 2020 is not reliably completely masked.

Key features:
- automatic association of arc frames taken on-sky with nearby science frames with the same pointing
- GUI to adjust red/blue flux levels and splicing
- final data output is target_*.fits, where the suffix is a single letter denoting the spatial index of the object/trace
- manual extraction GUIs
- `dbsp_show` plotting script to quickly inspect final data output
- `dbsp_adjust_splicing` to inspect and manually adjust splicing as needed for crowded fields and extended objects