* use `termion` rather than `ncurses` to limit runtime deps
* cross-compile with `cross` instead of our own dockerfiles/scripts
* update instructions
* update release procedure and GitHub actions to match
* prep changelog for `v0.7.8`
Fixes#160Closes#265
This is optional but now enabled for release builds.
Why?
* It shrinks the release docker images a bit, as the binary
includes only the gzipped version of files and uncompressed into RAM
at startup (which should be fast).
* It's a step toward #160.
