[seqfan] Erich Friedman links all repaired (I hope)

[Neil Sloane]

Dear Sequence Fans,
Erich Friedman moved all his pages to github (I gather it took a whole day
and was a maximally tedious and unpleasant task).

He sent me instructions on how to correct the links.  I was able to do
some of the work with global edits, and then by fine-tuning the tricky
ones by hand.

If someone would like to do some checking, that would be nice.

I can also send his instructions to anyone who is interested (but I hope
all the work has been done)