Add support for giving servers via command line or environment.

This also includes new API calls etcd_open_str and etcd_open_str.  The old
array-based calls are still available.

Signed-off-by: Jeff Darcy <jdarcy@redhat.com>
Add watch function.

Includes index support, both in and out.

Signed-off-by: Jeff Darcy <jdarcy@redhat.com>