bail on output failure; use fail bin to help track nEvents, a la master
skimmer efficiency calculation uses event counts
describe behavior
analysis to test skim eff
test that non-skimmed and skimmed yields match
mention test
say where printSkimResults should be called

Details:
just a note-to-self showing an example of how to use this feature.
Merge branch 'master' into skim-eff
Merge branch 'sample-info' into skim-eff
Merge pull request #185 from elaird/skim-eff

Skim eff
Merge pull request #187 from elaird/sample-info

Sample info