Publish developer binaries built with test/spec-bin.sh

[andychu]

This scripts builds stable version of bash/dash/mksh/zsh/busybox that we run spec tests against. This is the mitigation for issue #42.

It would be nice to make some portable Linux binaries so that everyone doesn't have to build them (or run Ubuntu 16.04).

Binaries to build:

• shells
• re2c -- to get rid of the pure Python path?
• A modified version of CPython that we run with? Not sure if this is necessary.

NOTE: We also use Clang, but their binary releases seem OK.

[andychu]

Several people have been able use test/spec-bin.sh, and we also have Nix in progress, so closing this