Asilib

- First merge of the Imager class. The `asilib.Imager` and `asilib.Conjunction` classes are still under development, but you can try it out! Call the `asilib.themis()` function to play around with an Imager instance.
- Removed the deprecated functions. Once Imager is fully implemented, most of the original functions will be deprecated.

- Removed the cartopy dependency. While some users were able to install it, overall it proved to be difficult to reliably build across multiple operating systems. Instead, I use the pyshp pure python library to read in the Esri shapefile files to make the map. Currently, only the mercator projection is supported. However, in the future, I plan to add other projections such as orthographic.
- Renamed asilib.create_cartopy_map() to asilib.make_map()

- Added a `path` kwarg to `keogram` and `plot_keogram` to create a keogram along a custom (lat, lon) path.
- Clarified the documentation.

- Added `animate_map` and `animate_map_generator` functions to asilib. I also added examples to the examples and tutorial sections of the docs.
- Added a warning in `equal_area` if the lat/lon values are outside of the skymap range.

- Renamed and deprecated `plot_movie` and `plot_movie_generator` for `animate_fisheye` and `animate_fisheye_generator` functions. This change is necessary for consistency with new functions such as `animate_map` and `animate_map_generator` functions.
- Updated the examples.
- Combined the download functions to `download_image` and `download_skymap`.

- Renamed the `_make_map` function to `create_cartopy_map()` so users can use this function to create maps from now on.
- Updated the information in `CONTRIBUTE.md`.