fix many internal links

Fixed a number of internal links that need to
go to the GitHub site.

Ran `make www` to perform the above.

2000/rince/README.md

@@ -81,7 +81,7 @@ Julian day number (given as a fractional component). E.g.:
 A Julian day is defined to be the number of days since January 1st in the year
 `-4712 (4713BC)`, starting at 12 noon GMT.[^1][^2] To aid conversion from our time
 (GMT) to Julian day there is a supplementary program named:
-[dmy2jd.c](dmy2jd.c). Run it with `day_float month year` as arguments. See below
+[dmy2jd.c](%%REPO_URL%%/2000/rince/dmy2jd.c). Run it with `day_float month year` as arguments. See below
 for an example.