Cleanup 4way interface

- implement cleaner interface into Cleanfligh
- separate initialization and start
- allow direct access to command processing, skipping BLHeli serial
   framing
- remove mspPort_t dependency
- refactor naming to CF style
- use serial_4way_impl.h for internal interface to bootloader
    implementation
- use uint16_t instead of hi/lo bytes ; use integer lengths
    instead of 0=256 encoding
- fix buffer overflow in stkv2 code

src/main/io/serial_msp.c

@@ -1568,7 +1568,7 @@ static bool processInCommand(void)
         // switch all motor lines HI
         // reply the count of ESC found
         headSerialReply(1);
-        serialize8(Initialize4WayInterface());
+        serialize8(esc4wayInit());
         // because we do not come back after calling Process4WayInterface
         // proceed with a success reply first
         tailSerialReply();
@@ -1579,7 +1579,7 @@ static bool processInCommand(void)
         // rem: App: Wait at least appx. 500 ms for BLHeli to jump into
         // bootloader mode before try to connect any ESC
         // Start to activate here
-        Process4WayInterface(currentPort, writer);
+        esc4wayProcess(currentPort->port);
         // former used MSP uart is still active
         // proceed as usual with MSP commands
         break;