[CLIENT] Added `transport_options` to list of client parameters

Updated the Transport::Client#initialize to accept a `transport_options` Hash,
and updated the Faraday connection constructor to pass them through.

This allows for full access to Faraday options:

client = Elasticsearch:Client.new \
           :host => 'yourcluster.address.com',
           :transport_options => {
             :request => { :open_timeout => 1 },
             :ssl     => { :verify => false }
           }

Closes #24
[CLIENT] Added a test for passing `transport_options` to the Faraday constructor

Adding tests for 3febc77 and tweaking the RDoc annotation

Related: #24
[CLIENT] Added, that Faraday connection parameters are merged into the request

This allows e.g. setting the default response format:

    client = Elasticsearch::Client.new \
               transport_options: { params: { format: 'yaml' } },
               log: true;

    client.info

    # 2014-02-10 19:08:08 +0100: GET http://localhost:9200/?format=yaml [status:200, request:0.006s, query:n/a]
    # ...
    # => "---\nstatus: 200\nname: \"Immortus\"\n..."

    YAML.load(client.info)['name']

    # => "Immortus"

Related: #24