feat: FlowControl: add FromStr impl

Allow creating a 'FlowControl' enum from a 'str' type. This is useful
when parsing strings from config files or command line arguments.

src/lib.rs

@@ -36,6 +36,7 @@ use std::convert::From;
 use std::error::Error as StdError;
 use std::fmt;
 use std::io;
+use std::str::FromStr;
 use std::time::Duration;
 
 #[cfg(unix)]
@@ -284,6 +285,19 @@ impl fmt::Display for FlowControl {
     }
 }
 
+impl FromStr for FlowControl {
+    type Err = ();
+
+    fn from_str(s: &str) -> std::prelude::v1::Result<Self, Self::Err> {
+        match s {
+            "None" | "none" | "n" => Ok(FlowControl::None),
+            "Software" | "software" | "SW" | "sw" | "s" => Ok(FlowControl::Software),
+            "Hardware" | "hardware" | "HW" | "hw" | "h" => Ok(FlowControl::Hardware),
+            _ => Err(()),
+        }
+    }
+}
+
 /// Specifies which buffer or buffers to purge when calling [`clear`]
 ///
 /// [`clear`]: trait.SerialPort.html#tymethod.clear