col_select doesn't work with selection helpers

[Moohan]

col_select should work with selection helpers, e.g. it should be possible to do get_spd(col_select = c("pc7", dplyr::starts_with("hscp")) but this doesn't work. I guess it's something to do with how it's being passed between functions and tied up with 'non-standard evaluation' etc. which just hurts my head!

[Nic-Chr]

Try replacing !!col_select with {{ col_select }}. I think the former can theoretically also only work with 1 column.

[Nic-Chr]

I've hopefully fixed the issue in the new PR #9