doc: add a design for the distributed database

Signed-off-by: David Scott <dave.scott@citrix.com>
doc: add a futures index

Signed-off-by: David Scott <dave.scott@citrix.com>
docs: fix the formatting of the distributed database proposed design

Signed-off-by: David Scott <dave.scott@citrix.com>
docs: improve the prototype description

Signed-off-by: David Scott <dave.scott@citrix.com>
Merge pull request #2013 from djs55/lots-of-docs

doc: add a design for the distributed database