snapshot
"Fix" make dependency

target/mbwatch target does not have inputs, so make does not know
when to rebuild the program. Regardless, this is better than always
rebuilding; we will have to document the use of `clean` or `make -B` to
force rebuilds.
Clarify some docstrings, comments
++todo
Don't bother with :as cell
Add --debug option
Remove colon from options summary

Resulting table is pretty sparse, but not imcomprehensible. We could add
options to customize the output table
Convert poll to ms in option's parse-fn
s/\bsignal\b/wakeup-signal/g

To elucidate purpose
++todo
Refactor config/render
++todo
config/stores -> store-name
Extract make-properties from imaps/with-connection
Add config/server
Restrict coordination to wait/notify signaling

Decomplect syncing, scheduling, connectivity polling, and looping. Use
only object signals for communication, not ref-watchers.

The run! function is longer now, but easier to understand.
Extract network/all-reachable?

Waiting for all results from network io is a perfect job for pmap.
++todo
Fix optparse doc
++todo