Asilib

Added
- The Mid-latitude All-sky-imaging Network for Geophysical Observations (MANGO) ASI array data loader.
- MANGO tests and documentation

Changed
- Updated the global coverage map with MANGO.

Changed
- The `_pcolormesh_nan()` function in the imager.py module. This function incorrectly handled skymaps whose FOV was clipped by the CCD at one or more edges (e.g., TREx-RGB). The new implementation includes a `Skymap_Cleaner()` class that handles both: the low elevation masking, as well as removing NaNs from the (lat, lon) skymaps. Removing NaNs is similar to the old implementation, but is now done in polar coordinates. This change necessitated numerous minor refactoring changes in `imager.py` and `imagers.py`.

Changed
- Removed all deprecated asilib functions and their documentation.
- Incremented the pandas version on `docs/requirements.txt` to fix an issue with readthedocs not compiling.

Added
- Added a kwarg to `asilib.asi.rego()`, `asilib.asi.trex_rgb()`, and `asilib.asi.trex_nir()`: acknowledge, which prints the acknowledgement everytime a new imager is loaded rather than once a month.
- Removed acknowledge.py
- Changed tests for acknowledgements

Added
- The `asilib.acknowledge.acknowledge()` function. It should be called by each loader to print that ASI's acknowledgment statement either when 1) the first time the user calls the function, or 2) when it has been a month since it was last called.
- Tests for `asilib.acknowledge.acknowledge()`.
- Added the call to `asilib.acknowledge.acknowledge()` in `asilib.asi.rego()`, `asilib.asi.trex_rgb()`, and `asilib.asi.trex_nir()`.

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`.