even simpler data storage

The data for each curve is now stored as one big string that has ALL the data;
this string is easily sent to gnuplot at once. There's also a bit of attached
meta-data to allow streaming --xlen culling to work
timefmt plots now work with streaming and with --xlen
reordered bash completion entries in alphabetical order. removed duplicate --zlabel
Updated bash, zsh completions with new commands. zsh completion has better prompts
added timefmt documentation
reformatted docs. no content changes
slightly improved --timefmt documentation