d: add skeleton for the D language

Contributed by Oliver Mangold.
https://lists.gnu.org/archive/html/help-bison/2012-01/msg00000.html

* README-D.txt, d-skel.m4, d.m4, lalr1.d: New.

data/README-D.txt

@@ -0,0 +1,60 @@
+Some usage notes for the D Parser:
+
+- it is a port of the Java parser, so interface is very similar.
+
+- the lexer class needs to implement the interface 'Lexer' (similar to
+  java). It typically (depending on options) looks like this:
+
+public interface Lexer
+{
+  /**
+   * Method to retrieve the beginning position of the last scanned token.
+   * @return the position at which the last scanned token starts.  */
+  @property YYPosition startPos ();
+
+  /**
+   * Method to retrieve the ending position of the last scanned token.
+   * @return the first position beyond the last scanned token.  */
+  @property YYPosition endPos ();
+
+  /**
+   * Method to retrieve the semantic value of the last scanned token.
+   * @return the semantic value of the last scanned token.  */
+  @property YYSemanticType semanticVal ();
+
+  /**
+   * Entry point for the scanner.  Returns the token identifier corresponding
+   * to the next token and prepares to return the semantic value
+   * and beginning/ending positions of the token.
+   * @return the token identifier corresponding to the next token. */
+  YYTokenType yylex ();
+
+  /**
+   * Entry point for error reporting.  Emits an error
+   * referring to the given location in a user-defined way.
+   *
+   * @param loc The location of the element to which the
+   *                error message is related
+   * @param s The string for the error message.  */
+   void yyerror (YYLocation loc, string s);
+}
+
+- semantic types are handled by D usions (same as for C/C++ parsers)
+
+- the following (non-standard) %defines are supported:
+
+  %define package "<package_name>"
+  %define parser_class_name "my_class_name>"
+  %define position_type "my_position_type"
+  %define location_type "my_location_type"
+
+- the following declarations basically work like in C/C++:
+
+  %locations
+  %error-verbose
+  %parse-param
+  %initial-action
+  %code
+  %union
+
+- %destructor is not yet supported