Introduce the "tests results file" terminology

Start calling the files that store the results of a test suite execution
"tests results files".  No need to use a fancier name to represent this
concept.
Rename ~/.kyua/actions/ to ~/.kyua/results/

Actions are a name of the past.  We now have results files, so make
sure the directory that holds them reflects the correct name.
Rename --store to --results-file

With the removal of the actions, we do not have a unified store any
longer.  Instead, we have independent results files and therefore the
command-line flag to configure their location should reflect this new
nomenclature.  Make it so.