Support safe navigation operator

The safe navigation operator is an operator from the name,
but it's a variety of dot token for method calling.
So TkSAFENAV class inherited Token class instead of TkOp class.

Author: aycabta

lib/rdoc/ruby_lex.rb

@@ -668,16 +668,16 @@ def lex_init()
       end
     end
 
-    @OP.def_rule(".") do
+    @OP.def_rules(".", "&.") do
       |op, io|
       @lex_state = :EXPR_BEG
       if peek(0) =~ /[0-9]/
         ungetc
         identify_number
       else
-        # for "obj.if" etc.
+        # for "obj.if" or "obj&.if" etc.
         @lex_state = :EXPR_DOT
-        Token(TkDOT)
+        Token(op)
       end
     end
 

lib/rdoc/ruby_token.rb

@@ -401,6 +401,7 @@ def Token(token, value = nil)
 
     [:TkASSIGN,     Token,  "="],
     [:TkDOT,        Token,  "."],
+    [:TkSAFENAV,    Token,  "&."],
     [:TkLPAREN,     Token,  "("],  #(exp)
     [:TkLBRACK,     Token,  "["],  #[arry]
     [:TkLBRACE,     Token,  "{"],  #{hash}