d: create alias Symbol for YYParse.Symbol

* data/skeletons/lalr1.d: Here.
* doc/bison.texi: Document it.
* examples/d/calc/calc.y, examples/d/simple/calc.y: Adjust.
* tests/calc.at, tests/d.at, tests/scanner.at: Test it.

data/skeletons/d.m4

@@ -447,6 +447,14 @@ m4_define([b4_var_decls],
 m4_define([b4_var_decl],
           [    protected $1;])
 
+# b4_public_types_declare
+# -----------------------
+# Define the public types: token, semantic value, location, and so forth.
+# Depending on %define token_lex, may be output in the header or source file.
+m4_define([b4_public_types_declare],
+[[
+alias Symbol = ]b4_parser_class[.Symbol;
+]])
 
 # b4_symbol_type_define
 # ---------------------

data/skeletons/lalr1.d

@@ -75,7 +75,7 @@ public interface Lexer
    * to the next token and prepares to return the semantic value
    * ]b4_locations_if([and beginning/ending positions ])[of the token.
    * @@return the token identifier corresponding to the next token. */
-  ]b4_parser_class[.Symbol yylex ();
+  Symbol yylex ();
 
   /**
    * Entry point for error reporting.  Emits an error
@@ -95,6 +95,8 @@ public interface Lexer
 ]])[
 }
 
+]b4_public_types_declare[
+
 ]b4_locations_if([b4_position_type_if([[
 static assert(__traits(compiles,
               (new ]b4_position_type[[1])[0]=(new ]b4_position_type[[1])[0]),