refactor to allow later substitution of plot-data formatters, eg svg instead of gnuplot
fix problem where the first with an empty database captured no results
make Observation a subclass of Context, Example to create Observations instead, specrunner to create a Database and pass it down the line to the Observations. Add some 'language' to Spec (still speculative at this stage)
oops - missed one file for previous commit
running an example under control of a spec file sort-of works. Much cleanup pending.