The :default_headers plugin accepts a hash of headers, and overrides the #.default_headers method
in the response class to be a copy of the headers.
Note that when using this module, you should NOT attempt to mutate of the values set in the default headers hash.
Example:
plugin :default_headers, 'Content-Type': 'text/csv'You can modify the default headers later by loading the plugin again:
plugin :default_headers, 'Foo': 'bar'
plugin :default_headers, 'Bar': 'baz'#.default_headersThe default response headers to use for the current class.
#.default_headersGet the default headers from the related roda class.