Allow functions to take data frames instead of individual vectors

[austinj]

Obviously, not an urgent issue, but taking a data frame as the first argument and then specifying variable names instead of needing to pass individual vectors for each argument would make these functions easier to manipulate.

[austinj]

Apologies; by "these functions," I mean effect_size_MB() and effect_size_ABk().

[jepusto]

See http://adv-r.had.co.nz/Computing-on-the-language.html for techniques to address this.

[jepusto]

data(Saddler)

Saddler_quality <- subset(Saddler, measure=="writing quality")

# current usage
effect_size_MB(Saddler_quality$outcome, Saddler_quality$treatment,
               Saddler_quality$case, Saddler_quality$time)

# what we want:
effect_size_MB(data = Saddler_quality,
               outcome = outcome,
               treatment = treatment,
               id = case,
               time = time)

[jepusto]

Make sure to include a unit test.