Add support for notations with symbols starting with a number.

E.g.
Notation "0+" := None.

Printing was working but not parsing.

parsing/cLexer.ml

@@ -737,9 +737,11 @@ let rec next_token ~diff_mode loc s =
         IDENT id, set_loc_pos loc bp ep end
   | Some ('0'..'9') ->
       let n = NumTok.Unsigned.parse s in
-      let ep = Stream.count s in
       comment_stop bp;
-      (NUMBER n, set_loc_pos loc bp ep)
+      begin try find_keyword loc (NumTok.Unsigned.sprint n) bp s
+      with Not_found ->
+        let ep = Stream.count s in
+        NUMBER n, set_loc_pos loc bp ep end
   | Some '\"' ->
       Stream.junk s;
       let (loc, len) =

test-suite/output/Notations4.out

@@ -215,3 +215,7 @@ Some MyNone+
      : option (option ?A)
 where
 ?A : [ |- Type]
+0+
+     : option ?A
+where
+?A : [ |- Type]

test-suite/output/Notations4.v

@@ -483,3 +483,10 @@ Check MyNone+.
 Check Some MyNone+.
 
 End LeadingIdent.
+
+Module SymbolsStartingWithNumbers.
+
+Notation "0+" := None.
+Check 0+.
+
+End SymbolsStartingWithNumbers.