Added ability to specify arbitary Docker parameters

I have a number of containers that require Tty and Stdin to be set (equivalent of launching with docker run and the "-t" and "-i" flags). I added a 'parameters' option, so you can now send arbitary flags to the Docker API, e.g.

namespace :environment do
  task :common do
    ...
    set :status_endpoint, '/'
    set :parameters, { 'Tty' => true, 'OpenStdin' => true  }
  end

This was based off the v1.0.10 tag.