Add a DSL for the plus option parser

[Rob Donnelly]

options = parse_plus_options(plus_options) do
  name "command"
  synopsis "command [options]"
  description <<-EOF
    Multi-line
    description
  EOF

  option :option1 do
    description "This is the first option."
    default "default-value"
  end

  option :option_two do
    description "This is option two."
    default 5
  end

  extra <<-EOF
    Multi-line
    extra
  EOF
end