[Feature Request] col_types argument of read_delim should be linked with col_select

[mcarauta]

Regarding read_delim (and its peers), it would be great that, whenever col_select is used, the argument col_types should refer only to the variables described at the col_select argument instead of the variables from the orignal/full document. This would be good for two reasons: (1) it is a waste of resource being forced to describe the column types of the entire document whenever you are using/selecting a handfull of variables, (2) this becomes super important whenever you are loading multiple files and they have a different number of columns/variables, and you only want to load a few variables/columns that are common to all files.