Missing a doc overhaul and tests, but this deals with most of the
feature upgrades in the blueprint.
The shell version of pt-diskstats is now in bin has pt-diskstats-shell,
in case that's needed.
With this most of the interactive mode should be working.
pt_diskstats.pm has the documentation and can be used for testing,
which should be in the next commit.
This commit also includes the revamped command line options.
Mostly bits and pieces at the moments. ReadKeyMini is a portable-ish
Term::ReadKey. Used here by DiskstatsMenu, which is currently only
for show.
Diskstats has most of the logic of the old pt-diskstats, with parts
now implemented by the DiskstatsGroupBy* classes; The latter subclass
the former.
As mentioned at the start, this is a work in progress. In addition to to
not having all the parts attached, also missing are the data-gathering mode,
the command-line argument parsing, and a large amount of tests.
