mshumko/aurora-asi-lib: Added asilib.Imagers

[0.18.0] - 2023-07-22 Added <ul> <li><code>asilib.Imagers()</code> class to make mosaics and synchronize plotting multiple imagers. The first two methods implemented are:<ul> <li><code>asilib.Imagers.plot_fisheye()</code> to plot fisheye lens images from multiple imagers, and</li> <li><code>asilib.Imagers.plot_map()</code> to project images from multiple imagers onto a map. This method has an <code>overlap</code> kwarg that by default masks out the (lat, lon) skymaps that map to pixels that overlap with a neighboring imager. This is a surprisingly efficient method that needs to be run just once (tested for up to five imagers; I'm unsure how a 10 or a 20 imager array will fare).</li> </ul> </li> <li>Added plot tests for the two <code>Imagers</code> methods.</li> <li>Added an <code>Imagers()</code> description in the Get Started and API pages. ### Changed</li> <li>Refactored the Donovan+2008 auroral arc example to use <code>asilib.Imagers.plot_map()</code>.</li> <li>Added a check to allow custom <code>matplotlib.colors.Normalization</code> object to be passed for <code>color_norm</code>.</li> </ul&gt