Render leisure=bleachers ways.

Discussion held in
#3140
suggested `leisure=bleachers` rendering could be similar in style to
pedestrian areas or other human-access features.

That is precisely what this patch does.

Colors were chosen to be those of `highway=pedestrian` because they are
pretty neutral; as `leisure=bleachers` can be used in a number of
contexts (such as sport pitches and outdoor theaters), I believe this
reduces potential visual confusion.

Note that it only renders ways; though found in the wild,
`leisure=bleachers` nodes are not supposed to be used.

project.mml

@@ -109,7 +109,7 @@ Layer:
                                                     'brownfield', 'landfill', 'salt_pond', 'construction', 'plant_nursery', 'religious', 'flowerbed') THEN landuse END)) AS landuse,
               ('shop_' || (CASE WHEN shop IN ('mall') AND (tags->'location' NOT IN ('underground') OR (tags->'location') IS NULL) THEN shop END)) AS shop,
               ('leisure_' || (CASE WHEN leisure IN ('swimming_pool', 'playground', 'park', 'garden',
-                                                    'golf_course', 'miniature_golf', 'sports_centre', 'stadium', 'pitch', 'ice_rink',
+                                                    'golf_course', 'miniature_golf', 'sports_centre', 'stadium', 'pitch', 'bleachers', 'ice_rink',
                                                     'track', 'dog_park', 'fitness_station', 'water_park') THEN leisure END)) AS leisure,
               ('man_made_' || (CASE WHEN man_made IN ('works', 'wastewater_plant', 'water_works') THEN man_made END)) AS man_made,
               ('natural_' || (CASE WHEN "natural" IN ('beach', 'shoal', 'heath', 'grassland', 'wood', 'sand', 'scree', 'shingle', 'bare_rock', 'scrub') THEN "natural" END)) AS "natural",
@@ -1598,7 +1598,7 @@ Layer:
                 'shop' || CASE WHEN shop IN ('yes', 'no', 'vacant', 'closed', 'disused', 'empty') OR shop IS NULL THEN NULL ELSE '' END,
                 'leisure_' || CASE WHEN leisure IN ('amusement_arcade', 'beach_resort', 'bird_hide', 'bowling_alley', 'dog_park', 'firepit', 'fishing',
                                                     'fitness_centre', 'fitness_station', 'garden', 'golf_course', 'ice_rink', 'marina', 'miniature_golf',
-                                                    'outdoor_seating', 'park', 'picnic_table', 'pitch', 'playground',
+                                                    'outdoor_seating', 'park', 'picnic_table', 'pitch', 'bleachers', 'playground',
                                                     'sauna', 'slipway', 'sports_centre', 'stadium', 'swimming_area', 'swimming_pool', 'track', 'water_park') THEN leisure END,
                 'power_' || CASE WHEN power IN ('plant', 'generator', 'substation') THEN power END,
                 'man_made_' || CASE WHEN (man_made IN ('chimney', 'communications_tower', 'crane', 'lighthouse', 'mast', 'obelisk', 'silo', 'storage_tank',

style/landcover.mss

@@ -721,6 +721,15 @@
     [way_pixels >= 4]  { polygon-gamma: 0.75; }
     [way_pixels >= 64] { polygon-gamma: 0.3;  }
   }
+
+  [feature = 'leisure_bleachers'][zoom >= 10] {
+    polygon-fill: @pedestrian-fill;
+    [zoom >= 15] {
+      line-width: 0.5;
+      line-opacity: 0.25;
+      line-color: @pedestrian-casing;
+    }
+  }
 }
 }