This call appears to only be necessary because reset() was called from
NewMaterializer.
This commit has the constructor set a default value for updateCh, and
removes both the call to reset() from New(), and the call to
notifyUpdateLocked() from reset().
This should ensure that we do not notify the Fetch() call before we have new
values to report.
Refactor of Materializer.Run
Use handlers to manage state in Materializer
Rename Materializer receiver
rename m.l to m.lock, and flip some conditionals to remove the negative.
Improve godoc, rename Deps, move resetErr, and pass err into notifyUpdate
Update for NewSnapshotToFollow events
Refactor to move context cancel out of Materializer
