Expand MapCSS grammar for supporting layer selectors

Not used in any way yet though.

autotests/data/mapcss/parser-test.mapcss

@@ -121,3 +121,16 @@ node[shop=pastry]
 node.importantShops { color: "red"; }
 way.importantShops|z20- { color: "green"; }
 *.importantShops[access=no] { color: "blue"; }
+
+// layer selectors (see https://wiki.openstreetmap.org/wiki/MapCSS/0.2/Proposal_layer_selector)
+way[highway]::road {
+  width: 8;
+  color: #ffffff;
+  casing-width: 2;
+  casing-color: #a0a0a0;
+}
+way[railway=tram]::tram {
+  width: 2;
+  color: #303030;
+  z-index: 1;
+}

autotests/data/mapcss/parser-test.mapcss.ref

@@ -142,3 +142,18 @@ way.importantShops|z20-
     color: "blue";
 }
 
+way[highway]
+{
+    width: 8;
+    color: #ffffffff;
+    casing-width: 2;
+    casing-color: #ffa0a0a0;
+}
+
+way[railway=tram]
+{
+    width: 2;
+    color: #ff303030;
+    z-index: 1;
+}
+

src/map/style/mapcssparser.y

@@ -119,6 +119,7 @@ using namespace KOSMIndoorMap;
 %type <zoomRange> ZoomRange
 %type <condition> Condition
 %type <binaryOp> BinaryOp
+%type <strRef> LayerSelector
 %type <strRef> Key
 %type <rule> Declarations
 %type <declaration> Declaration
@@ -189,14 +190,14 @@ Selector:
 
 // TODO incomplete: missing pseudo-class
 BasicSelector:
-  T_IDENT[I] ClassSelector[C] ZoomRange[Z] Tests[T] {
+  T_IDENT[I] ClassSelector[C] ZoomRange[Z] Tests[T] LayerSelector[L] {
     $$ = new MapCSSBasicSelector;
     $$->setClass($C.str, $C.len);
     $$->setObjectType($I.str, $I.len);
     $$->setZoomRange($Z.low, $Z.high);
     $$->setConditions($T);
   }
-| T_STAR ClassSelector[C] ZoomRange[Z] Tests[T] {
+| T_STAR ClassSelector[C] ZoomRange[Z] Tests[T] LayerSelector[L] {
     $$ = new MapCSSBasicSelector;
     $$->objectType = MapCSSBasicSelector::Any;
     $$->setClass($C.str, $C.len);
@@ -236,6 +237,11 @@ BinaryOp:
   T_BINARY_OP { $$ = $1; }
 | T_EQUALS    { $$ = MapCSSCondition::Equal; }
 
+LayerSelector:
+  %empty { $$.str = nullptr; $$.len = 0; }
+| T_COLON T_COLON T_IDENT[L] { $$ = $L; }
+;
+
 Key:
   T_IDENT { $$ = $1; }
 | Key T_COLON T_IDENT { $$.str = $1.str; $$.len = $3.str - $1.str + $3.len; }