- (WGI|WSF)_RESPONSE(*) renamed write_headers_string as write_header_text

- HTTP_HEADER.string does not have the ending CRLFCRLF .. but just CRLF
- WGI_RESPONSE.write_header_text has the responsibility to handle the last blank line CRLF (separating the header from the message)
- HTTP_HEADER.string does not set anymore a default content type as text/html
- added WGI_RESPONSE.write_header_lines (ITERABLE [TUPLE [name,value: READABLE_STRING_8]] mainly as an helper method,
   this way the WGI user does not have to know about the CRLF end of line

library/server/ewsgi/examples/hello_world/src/hello_world.e

@@ -20,7 +20,8 @@ feature {NONE} -- Initialization
 
 	execute (req: WGI_REQUEST; res: WGI_RESPONSE)
 		do
-			res.write_header (200, <<["Content-Type", "text/plain"]>>)
+			res.set_status_code (200)
+			res.write_header_lines (<<["Content-Type: text/plain"]>>)
 			res.write_string ("Hello World!%N")
 		end