Scripting lesson from NESCent's May 8-9, 2014 workshop.

The lesson started from SWC material on shell scripting, but subsequently
underwent a large-scale rewrite and partial reorganization and narrowing
to strictly focus on shell scripting for building executable data pipelines.
Full history is at NESCent/2014-05-08-datacarpentry@@a372d81 and preceding
commits from me.
Merge pull request #19 from datacarpentry/scripting-lesson

Scripting lesson from NESCent's May 8-9, 2014 workshop.