allow outputting a directory tree of logs that follows the shell function stack

[andychu]

"automatic, hierarchical logging that follows shell function stack"

All the spew from build/dev.sh all got me thinking about this.

It would be nice to retain logs, but in a more structured way that doesn't have spew.

I can see this being very useful for continuous builds. They want to save lots and not "shut things up". And in fact "toil" saves a lot of logs on its own. The shell could fairly easily do this

---

Example: each of these would gets its own file. And then there is some UI on top of it. It's directory tree of logs.

build() {
   build-yajl
   build-libc
}

test() {
  tests-to-run | xargs -- $0 run-one-test
}

main() {
  build
  test
}

[andychu]

Another way to phrase this is to fix the fact that you write shell scripts in YAML with .travis.yaml

The only reason to do this is separate logging!!

[andychu]

This is pretty much #583 and related to #882