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* Add ephemeris objects that are propagated with the Lagrange interpolator.
* Add Cesium CZML output. Set sim option `save_czml` to `false` to disable.
* Add CSV text file star catalog loader. This feature is useful for small catalogs such as Hipparcos and simulating wide FOV sensors.
* Add multiplier and clipping for radial cosine.
* Add option to skip image rendering. Set sim option `mode` to `none` to bypass image rendering.
* Update interfaces for newest version of Skyfield, Poliastro, POPPY, and AstroPy.
* Fix star renderer issue removing stars in field of view for non-square arrays.