Added support for base URL

I've been looking at a few different ES hosts, and noticed that some of them (e.g. qbox.io) add a namespace path before the index portion of the path, which makes them incompatible with Elastical as it stands.

e.g.

    curl -X PUT http://api.qbox.io/namespaceName/indexName -d '{
        "number_of_shards" : 4,
        "number_of_replicas" : 1
    }'

This change adds a simple option to allow Elastical to be configured to support base paths