Add a CHANGES.md file, prep for 0.0.2 release (linkerd#12)

Make the namerd stream resilient to failures (linkerd#7)

Recently the semantics of `futures::Stream` changed such that errors are
terminal.

Now, we ensure that individual namerd request failures are not propagated onto
the address stream.

Furthermore, configuration files have been made more brittle so that unknown
fields are not silently ignored.