[EXTENSIONS] Added the `ANSI` extension

Colorize and format Elasticsearch responses à la Elasticat [http://git.io/elasticat]:

    require 'elasticsearch/extensions/ansi'

    puts Elasticsearch::Client.new.cluster.state.to_ansi

    puts Elasticsearch::Client.new.search.to_ansi

    puts Elasticsearch::Client.new.indices.analyze(text: 'Quick Brown Fox Jumped').to_ansi