Add ggsky extension (#223)

* Add ggsky extension

* change short descr

Author: uskovgs

_config.yml

@@ -2352,3 +2352,17 @@ widgets:
    2. Draw theoretical limits for proportion (0 to 1). 3. Calculate proportion and place it in the logical limits (i.e. the balancing point for stacks).  
    4. Place null within the logical limits  5. Draw distribution for NULL and standard deviations within the distribution.  6. determine the z-score (where does observed prop fit into NULL distributions) 
    (i.e. how many standard deviations fit between .5 and .67)
+
+- name: ggsky
+  thumbnail: images/ggsky.png
+  url: https://uskovgs.github.io/ggsky
+  ghuser: uskovgs
+  ghrepo: ggsky
+  tags: visualization,astronomy,coordinates,projection,axis
+  cran: false
+  ghauthor: uskovgs
+  short: >
+    Draw all-sky maps in Galactic or equatorial coordinates with a Hammer-Aitoff projection
+  description: >
+   ggsky extends ggplot2 with `coord_galactic()` and `coord_equatorial()` for making sky maps in a Hammer-Aitoff projection.
+   It includes helper scales (scale_gal_lon/scale_gal_lat and scale_eq_ra/scale_eq_dec) to control graticule breaks and label formatting (including RA in hours).