Figure out how to collect messages for the user during tasks

[arrdem]

At present, the :msg and {:intent :msg ...} behavior is really magical and intended only for use by task implementers with specific behavior in mind. "logging" ala clojure.tools.logging sucks because people choose not to participate in it - eg depstar which sorta rolls its own structured logging using prn.

Really I need a reasonable composing pattern for capturing the *out* and *err* lines as well as other somewhat structured messages from tasks so that the :msg field can be automatically populated for tasks like compile which really have a lot to even without explicitly capturing and passing output to the user.