def field(name, **options)
      name = name.to_sym
      definitions[name] = options
      proxy.instance_eval do
        define_method(name) { fields[name] }
        define_method("#{name}=") { |value| fields[name] = value }
      end
    end
def field(name, **options)
      name = name.to_sym
      definitions[name] = options
      proxy.instance_eval do
        define_method(name) { fields[name] }
        define_method("#{name}=") { |value| fields[name] = value }
      end
    end
Declare new form field

 @param [Symbol] name Field name
 @param [Hash] options Options
 @option (see Ciesta::Field)