improve bin/new-year.sh and Makefile sub-dir processing

The `bin/new-year.sh` now uses make rules to perform some
if its actions.  It modifies the `Makefile` to add the
new year to the `${YEARS}` make variable.

Changed `bin/new-year.sh` VERSION from "1.0 2024-07-21"
to "1.1 2024-07-21".

The top level `Makefile` will test of a Makefile for
a given year exits before calling a make rule for the year.
If there is no `YYYY/Makefile` a warning message is issued

Updated `bin/README.md` to reflect these changes.

Performed `make www` to accomplish the above and to test under macOS.

bin/README.md

@@ -583,9 +583,7 @@ For example:
 
 ``` <!---sh-->
     mkdir -p YYYY
-    chmod +w .top
-    bin/new-year.sh YYYY
-    chmod -w .top
+    bin/new-year.sh -v 1 YYYY
 ```
 
 Here, `YYYY` must be a new 4-digit IOCCC year.