USB comm: prepare for @micolous change (PR#463) (#587)

* move communication related code from proxmark3.c and cmdmain.c to new file comms.c
* replace byte_t by uint8_t in uart_posix.c and uart_win32.c
* move OpenProxmark() and CloseProxmark() from flasher.c to flash.c
* move print_lock mutex including initializer to ui.c
* minor changes in printing help texts
* no changes in comms functionality yet

uart/uart.h

@@ -39,7 +39,15 @@
 #include <stdint.h>
 #include <stdbool.h>
 
-typedef unsigned char byte_t;
+/* Used to substitute for an example serial port path on each platform.
+ */
+#ifdef _WIN32
+#define SERIAL_PORT_H	"com3"
+#elif __APPLE__
+#define SERIAL_PORT_H	"/dev/tty.usbmodem*"
+#else
+#define SERIAL_PORT_H	"/dev/ttyACM0"
+#endif
 
 /* serial_port is declared as a void*, which you should cast to whatever type
  * makes sense to your connection method. Both the posix and win32
@@ -78,13 +86,13 @@ void uart_close(const serial_port sp);
  * partial read may have completed into the buffer by the corresponding
  * implementation, so pszRxLen should be checked to see if any data was written. 
  */
-bool uart_receive(const serial_port sp, byte_t* pbtRx, size_t pszMaxRxLen, size_t* pszRxLen);
+bool uart_receive(const serial_port sp, uint8_t* pbtRx, size_t pszMaxRxLen, size_t* pszRxLen);
 
 /* Sends a buffer to a given serial port.
  *   pbtTx: A pointer to a buffer containing the data to send.
  *   szTxLen: The amount of data to be sent.
  */
-bool uart_send(const serial_port sp, const byte_t* pbtTx, const size_t szTxLen);
+bool uart_send(const serial_port sp, const uint8_t* pbtTx, const size_t szTxLen);
 
 /* Sets the current speed of the serial port, in baud.
  */