upspin: add straw man interface definitions
upspin: add straw man interface definitions

New package.

A proposal. Everything is open to debate.

Change-Id: Ie1a8397064574a220b710695e8b98f7de1dd0efd
Reviewed-on: https://upspin-review.git.corp.google.com/1022
Reviewed-by: Eduardo Pinheiro <55040cbb39ba395339ae7940d8da6cd97797a4a8@google.com>

upspin/upspin,upspin/upspin