Added Function2 versions of map/flatMap.
Update docs to reflect that Editor is now global.
Added general mechanism for visiting a list of locs.

Many things generate a list of (store, offset) pairs which one wants to cycle
through, so it's nice to both have a standard set of key bindings to navigate
the list and a standard mechanism for said list generators to plug into.
Added Signal.apply(Executor).

This allows one to easily create a signal which dispatches emitted events via a
particular executor (usually the UI thread executor).
Revamped SubProcess to be event based.

This also includes events to indicate that stdout and stderr have "completed"
(we detected EOF on them).

Lacking those made it difficult to know when your subprocess was done
generating output. Using waitFor was insufficient because that could return
before the final output was read from the process (by a background thread).
Line.Builder tweak.