Create average-link-strength-1948-2013.txt

The second column in this file lists the average link strengths S as computed by `ludescher.R` at 10-day intervals, starting from day 730, and going until day 24090, where day 1 is the first of January 1948. The first column numbers these items from 1 to 2337. For an explanation see [Part 4](http://johncarlosbaez.wordpress.com/2014/07/08/el-nino-project-part-4/) of the El Niño Project series.