Inconsistent "indexed-ness" for columns when using within and outside a proc-macro environment

This crates docs for [`LineColumn`](https://docs.rs/proc-macro2/latest/proc_macro2/struct.LineColumn.html) say that the column is 0-indexed. The docs for [`proc_macro::LineColumn`](https://doc.rust-lang.org/proc_macro/struct.LineColumn.html) say that the column is 1-indexed. As far as I can see, this is a documentation issue in proc_macro2 and the column value from the `proc_macro::LineColumn` is used without offset.