Add package to CRAN

[benwhalley]

Do you have a view on getting apastats onto CRAN? Would you be open to pull requests to achieve it?

[achetverikov]

I have nothing against it, just wasn't sure if it's actually useful enough. Probably some stuff needs to be dropped (like lmer_with_julia) and some stuff triple checked (like plot.pointrange). And thanks for the first-ever pull request for this package!