handle zero-result queries, specify index/type, add stub of rspec

Attempting to aggregate several PRs, feature requests and issues:

https://github.com/elasticsearch/logstash-contrib/pull/57
https://github.com/elasticsearch/logstash-contrib/issues/95
https://github.com/elasticsearch/logstash-contrib/pull/96

with help and input from @greem @sisutcliffe @bleskes et al.

I'll clarify; sorry for being obtuse!

doing `:default => ""` is fine for code execution, but in the documentation it will read that the default index is an empty string. As an Elasticsearch user, this confuses me slightly because I don't know what this really means. Instead, I think it would be better to remove the :default setting andalso detailing the default behavior if-not-specified.

Same for :type, whatever we call that setting later.