version: add a API method that returns the server version

The point of this API method, besides giving server end users the
information, is to allow client applications to adapt to server
versions, or more simply just require a given version and bail out
if that is not present.

Signed-off-by: Cleber Rosa <crosa@redhat.com>
Merge pull request #10 from clebergnu/version

version: add a API method that returns the server version