Rename generic layer.sql to actual_layer_name .sql (#1034)

Following layers had generic `layer.sql` name.

- `aerodrome_label`
- `aeroway`
- `housenumber`
- `mountain_peak`
- `park`
- `place`
- `poi`
- `transportation`
- `transportation_name`
- `water_name`

This PR renames `layer.sql` to `aerodrome_label.sql`, `aeroway.sql`...

layers/housenumber/housenumber.sql

@@ -0,0 +1,23 @@
+-- etldoc: layer_housenumber[shape=record fillcolor=lightpink, style="rounded,filled",
+-- etldoc:     label="layer_housenumber | <z14_> z14+" ] ;
+
+CREATE OR REPLACE FUNCTION layer_housenumber(bbox geometry, zoom_level integer)
+    RETURNS TABLE
+            (
+                osm_id      bigint,
+                geometry    geometry,
+                housenumber text
+            )
+AS
+$$
+SELECT
+    -- etldoc: osm_housenumber_point -> layer_housenumber:z14_
+    osm_id,
+    geometry,
+    housenumber
+FROM osm_housenumber_point
+WHERE zoom_level >= 14
+  AND geometry && bbox;
+$$ LANGUAGE SQL STABLE
+                -- STRICT
+                PARALLEL SAFE;