All declared Imports should be used

[jamesmbaazam]

From a devtools::check() run, we need to fix this. I think this ties loosely with #82. Basically, adding @importFrom(<pkg>, <function>) to the roxygen2 tags should fix it. I'm happy to submit a PR to fix it. Do let me know.

>devtools::check()

> checking dependencies in R code ... NOTE
  Namespaces in Imports field not imported from:
    ‘RcppParallel’ ‘config’ ‘devtools’ ‘gsubfn’ ‘jsonlite’ ‘purrr’ ‘qtl’
    ‘reshape2’ ‘rstantools’ ‘tidyverse’ ‘usethis’ ‘vdiffr’