Add flow control switches to serialport (#579)

* Fix alignment of baud rate setting.

* Add flow control flags DTR and RTS.

* Add flags for flow control RTS and DTR.

* Add pin states for flow control flags

* Change pinstates to linestates

* Remove help text about DTR/RTS defaulting to low.

* Collect flow control setting into one single command.

* Add curly braces.

* Add more curly braces.

* Add CTS and DSR settings. Add default none option. Change settings layout for flow control.

io/serialport/locales/en-US/25-serial.json

@@ -33,6 +33,11 @@
             "odd": "Odd",
             "space": "Space"
         },
+        "linestates": {
+            "none": "",
+            "high": "High",
+            "low": "Low"
+        },
         "split": {
             "character": "on the character",
             "timeout": "after a timeout of",