Create general pre-processing function for internal use

[hanneoberman]

[hanneoberman]

If the vrb argument will be deprecated, use https://lifecycle.r-lib.org/reference/index.html

[hanneoberman]

See also: http://adv-r.had.co.nz/Computing-on-the-language.html and https://adv-r.hadley.nz/meta-big-picture.html

[hanneoberman]

Use shorthand for NULL defaults: https://design.tidyverse.org/def-short.html?q=%25%7C%7C%25#arg-short-null

[hanneoberman]

Fixed in #94

[hanneoberman]

@pepijnvink Please split this up into verify_df, verify_mids, etc.

[hanneoberman]

Opties voor ggmice

• if(check_df en check_mids) {als error, then ggmice requires df or mids`}
• use inherits() en any()