read byte feature add

Sources/SwiftSerial.swift

@@ -461,7 +461,22 @@ extension SerialPort {
                 return character     
             }
         }
+    }
     
+    public func readByte() throws -> UInt8 {
+        let buffer = UnsafeMutablePointer<UInt8>.allocate(capacity: 1)
+        
+        defer {
+            buffer.deallocate(capacity: 1)
+        }
+        
+        while true {
+            let bytesRead = try readBytes(into: buffer, size: 1)
+            
+            if bytesRead > 0 {
+                return buffer[0]
+            }
+        }
     }
 
 }