mapr is Unmaintained

The `mapr` fork has been merged back into upstream fork `memmap2`.

The maintainer(s) have advised `mapr` is deprecated and will not
receive any maintenance in favor of using `memmap2`.

## Possible Alternative(s)

The below list has not been vetted in any way and may or may not contain alternatives;

- [`memmap2`](https://github.com/RazrFalcon/memmap2-rs)