Created Histogram gallery category, modified conf.py and moved rose.py to new 'Histogram' category

Author: alperen-kilic

doc/conf.py

@@ -78,6 +78,7 @@
             "../examples/gallery/3d_plots",
             "../examples/gallery/seismology",
             "../examples/gallery/basemaps",
+            "../examples/gallery/histograms",
             "../examples/gallery/embellishments",
             "../examples/projections/azim",
             "../examples/projections/conic",

examples/gallery/histograms/README.txt

@@ -0,0 +1,2 @@
+Histograms
+----------