Lwt_unix: rename functions to 'open_client' and 'open_server'

We still need to support a more traditional client/server model by
having some kind of 'listen', 'accept' and 'connect'. This will need
to be built on top of 'open_client' and 'open_server'.

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Update the README instructions

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Update CHANGES

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Merge pull request #32 from djs55/api-changes

Improve API and read me