Asilib

Added
- `Imagers.animate_map()` and `Imagers.animate_map_gen()` methods to animate mosaics.
- `Imagers.__iter__()` to iterate over every imager synchronously. This won't work perfectly when you mix multiple imager arrays such as REGO and THEMIS, as their cadences are 6- and 3-seconds, respectively.
- `Imagers.__str__()` to print details regarding each ASI imager.
- Tests for the above methods.
- A warning in the Calgary downloader function if there was no image data locally or online.
- A mosaic animation example in the documentation.

Fixed
- A bug when no data from an hour exists and `asilib.Downloader()` crashed when it did not find the folder.

Changed
- Incremented the dependencies in `requirements.txt`.

Changed
- Renamed `aurora-asi-lib` to `asilib` in PyPI. Now the package can be installed via `python3 -m pip install asilib`.

Changed
- Edited the Acknowledgments section and clarified the source of skymap files.

Added
- Animate mosaics via `asilib.Imagers.animate_map()`. This method relies on synchronous iteration of all `asilib.Imager` objects passed into `asilib.Imagers`.
- Loop over images of all `asilib.Imager` objects passed into `asilib.Imagers` as a function of time via `asilib.Imagers__iter__()`. This method returns a valid time stamp and image for all time synchronized `asilib.Imager` images, and returns a placeholder `None` if an `asilib.Imager` is off, or the imager is not synchorized (closest time stamp is more than a cadence away in time).

Fixed
- Auroral intensities resulted in an index error is the satellite was at the horizon.

Changed
- Removed the RGB normalization in the `trex_rgb()` loader. This fixed the vertical stripes in the keograms, but made the fisheye and mapped images much darker (since the `norm` kwarg in `plt.pcolormesh` and `plt.imshow` does nothing).
- Refactored the TREx and Imager tests reflecting the minor changes.

Added
- A `color_brighten` kwarg to by default enhance the RGB colors when calling the following asilib.Imager methods, `plot_fisheye`, `animate_fisheye_gen`, `plot_map`, and `animate_map_gen`. Unless `color_brighten=False`, the plots remain the same.

Fixed
- A bug raised in issue 15 (https://github.com/mshumko/asilib/issues/15) where an `asilib.Imagers` class, initiated with a single `asilib.Imager`, would try to incorrectly index `asilib.Imager` unless it is wrapper in a tuple.