Spelunker

- Improvements and enhancements.

- Improvements and enhancements.

- Added ability to control number of bins in `timeseries_binned_plot.
- Changed Python requirements.

- Changes and improvements to `spelunker.load.guidestar_plot`.

- Added `if fov_radius.value == 0: fov_radius = 2*u.deg` to `spelunker.load.guidestar_plot` as recommended by hdiamondlowe from issue 19.
- Added GitHub actions for `general_test.py`.

- Added `jwstuser` to `setup.py`.