add function cbindlist

[MichaelChirico]

Inspired by this SO Q&A:

https://stackoverflow.com/q/48333523/3576984

dplyr::bind_cols syntax is appealingly clean.

cbindlist(X) would feel more data.table and provide the same functionality; even as a simple wrapper to setDT(unlist(X, recursive = FALSE)) this could be a nice convenience tool.

Not sure if there's any scope for further speedup under the hood as well.

[arunsrinivasan]

Pretty neat! I don't think there's any concern for speed here.. But if one were to do cbindlist(X)[, col := new_val], then col from X would be updated as well. Probably documenting it would be sufficient..

[MichaelChirico]

Duly noted, always good to remind side effects of mutability.

Would it be possible for setDT to do this internally, i.e. for setDT(X) to work (and be equally by-reference as setDT(unlist(X, recursive = FALSE))? Does it make sense for setDT to become that flexible, if so?