Add plugin release semi-automatic script

Closes #8.
Add plugin version in es-plugin.properties

With https://github.com/elasticsearch/elasticsearch/issues/2784, we can now add plugin version in `es-plugin.properties` file.

It will only be used with elasticsearch 1.0.0 and upper. No need to push it in 1.x branch.

Closes #9.
Update to elasticsearch 1.0.0

Closes #10.
Add documentation

Closes #2.