push .ascii namespace to stdlib

[Francis De Brabandere]

The readme mentions this

.ascii namespace, which should probably be pushed into the stdlib, once there's a process for doing that

Looks like this should be possible now
https://www.unisonweb.org/2020/04/25/april-update/#organizing-your-codebase

[Ian Denhardt]

Opened a PR: unisonweb/base#46

[Ian Denhardt]

PR has been merged, so this is available in base's trunk now. I'm going to leave this open until I get around to updating the README.