Formula input

[iwahiropuzzles]

Can you make aglm possible to accept a formula input as in glmnetUtils::glmnet?

[kkondo1981]

Just tried in #63.
I implemented formula versions of aglm() and predict() and it seems to work.
I'm wondering if avoiding model.frame() is better, and might need some performance check to determine it.
Will returned here after gathering demos for more datasets.