`readr` and `vroom` as a replacement of `read.fwf2`

[chainsawriot]

Actually, haven depends on readr for 6 years now.

https://github.com/tidyverse/haven/blob/9b3b21b5e9b64867eb53818faa7e9a22480f347d/DESCRIPTION#L25

And readr depends on vroom. We don't need this code to parse fwf files as readr can do this much faster.

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Actually, it also raises the question of whether we need datable::fread() and datatable::fwrite() anymore. But let's keep this discussion to fwf.

[chainsawriot]

Just reuse this old code

https://github.com/gesistsa/rio/blob/067a0ae805fdd96816fe9103af9f1843df3584a2/R/import_methods.R#L85-L126

[chainsawriot]

This whole bunch of code is barely tested.

https://github.com/gesistsa/rio/blob/840d27b5e00deef6ddd19ae138fb7404bc1b3ca3/R/export_methods.R#L42-L98