[seqfan] new format for links to b-files

[N. J. A. Sloane]

With a view to the future, we are changing the format for links to b-files.

The new format is illustrated by

%H A001620 T. D. Noe, <a href="b001620.txt">Table of n, a(n) for n=0..2000</a>
%H A139080 M. F. Hasler, <a href="b139080.txt">Table of n, a(n) for n=1,...,10000</a>.
%H A047999 T. D. Noe, <a href="b047999.txt">Rows n=0..50 of triangle, flattened</a> 

Please use format in the future!    Neil