GH-149: Added name support for revision statements.

[kittaakos]

So they will show up in the Outline.
The name will be the revision date.

Closes: #149.

Signed-off-by: Akos Kitta kittaakos@typefox.io

---

For reviewers:

Model:

module abc {
    yang-version 1.1;
    namespace abc;
    prefix a;
    revision 2018-10-10 {
          a:version 4;
          a:release 5;
          a:correction 6;
    }
    revision 2018-09-10 {
          a:version 1;
          a:release 2;
          a:correction 3;
    }
    extension version {
        argument value;
    }
    extension release {
        argument value;
    }
    extension correction {
        argument value;
    }
}

Before the change:

After the change:

[JanKoehnlein]

LGTM