Add png generation back in (using the imagemagick convert tool), add png files to gitignore

This is so we aren't committing binary data to the git repository if
that data may get updated in the future because I decide to make changes
to algorithms, palettes, etc. It's still nice to get the png files
generated so they can stay.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

tools/genexamples.sh

@@ -15,8 +15,8 @@ while read infile; do
             pngfile="examples/$(basename -s .in "$infile")-$hash-$matrix.png"
             echo "Generating $svgfile"
             python3 -m colorhash "$infile" --output-type svg --out "$svgfile" --hash "$hash" --matrix "$matrix"
-            #echo "Generating $pngfile"
-            #convert "$svgfile" "$pngfile"
+            echo "Generating $pngfile"
+            convert "$svgfile" "$pngfile"
         done
     done
 done