Update the design to mention our in-memory transport, since it is
generally useful, and update the implementation to use distinct types
for InMemoryTransport and StdIOTransport (the fact that they are both
implemented as an io.ReadWriteCloser is an implementation detail).
Change-Id: I8228ccf2092a56a730c113c4db105fb492cce112
Reviewed-on: https://go-review.googlesource.com/c/tools/+/672715
Reviewed-by: Sam Thanawalla <samthanawalla@google.com>
Commit-Queue: Robert Findley <rfindley@google.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
TryBot-Bypass: Robert Findley <rfindley@google.com>