fixes improper cv result averaging

previous code took quantiles for cv results for each computation and
then averaged the quantiles across all imputed data frames. this commit
combines cv results across all imputations and then takes
quantiles.
removes "do no circulate" warning
updates documentation, formatting, adds small abstraction

documentation improvments to the more complicated functions in cv.R and
all.R, updates to the readme to reflect these changes, indentation fix
in imp.R, cruft removal in plot.R.
makes cv function calls more terse

wraps call to CallCV in CleanCV, rather than doing the same thing on two lines
deletes a file I missed