let a stack compute its settings without make

A stack can now ship <name>.env and <name>.sh next to its compose files. The
hook is sourced with the tag helpers available, which is what the computing
.mk files of the catalogue were using make for: 29 of its 44 .mk files only
exist to build variables like the fabio tags.

Converting stack/host/fabio.mk by hand gives byte-identical output for the
route tag, and drops a trailing comma the make version left in the listener
list.

Also: APP_HOST and APP_URI are computed (the tag helpers build on them),
--color controls the escape codes rather than always emitting them, and
make test-portability runs the CLI under busybox ash and dash.

spec/golden/expected.cli/cat-unknown-target.txt

@@ -6,6 +6,7 @@ Options:
  -e ENV environment (default: local, or ENV from the config)
  -H HOSTS run on remote hosts instead (comma separated, or "all")
  -n, --dry-run print the commands instead of running them
+ --color WHEN always, never or auto (default: colour when on a terminal)
  -v, --verbose show what myos does
  -d, --debug show every command
  -h, --help this help