docker container with dosemu2.

Used by dex for those fun images that need dos such as [deltree](https://github.com/dockerland/dex-dockerfiles-extra/tree/master/dex-images/deltree and edit

• to support console auto-detection of keyboard layout, pass tty0

docker run briceburg/dosemu
^^^ opens c:\ -- use `exitemu` to exit

docker run --device=/dev/tty0 -e LANG=$LANG briceburg/dosemu
^^^ autodetects keyboard layout and passthru LANG

docker run briceburg/dosemu -dumb dir
^^^ outputs directory listing of c:\

exitemu to exit from dosemu

• compile on musl for alpine
• allow non-root user to read tty0, the SUID bit on dosemu did not fix.