Library for Sabertooth motor driver ported from the oficial Arduino library. Packetized Serial Mode

I ported the official arduino library for Sabertooth dual motor drivers. In the porting process I did not used const methods as the original library does, but the functionality stays the same. I also added some methods that I find useful. According to the documentation of the driver this code should be compatible with SyRen drivers.

Revision:
1:013fa8604413
Parent:
0:70797f033fe0
--- a/Sabertooth.cpp	Mon Feb 20 11:10:08 2017 +0000
+++ b/Sabertooth.cpp	Thu Sep 21 12:32:29 2017 +0300
@@ -127,12 +127,13 @@
   switch (baudRate)
   {
   case 2400:           value = 1; break;
-  case 9600:  default: value = 2; break;
+  case 9600:  default: value = 2; baudRate = 9600; break;
   case 19200:          value = 3; break;
   case 38400:          value = 4; break;
   case 115200:         value = 5; break;
   }
   command(15, value);
+  _sabertoothserial.baud(baudRate);
   // Sabertooth takes about 200 ms after setting the baud rate to
   // respond to commands again (it restarts).
   // So, this 500 ms wait should deal with this.