USB device stack; Added getter method for terminal_connected;

Fork of USBDevice by mbed official

Example of use:

#include "mbed.h"
#include "USBSerial.h"

USBSerial  pc;
DigitalOut blue_led(P0_20);

int main() {
    blue_led = 1;
    while(!pc.getTerminal_connected()); //Wait for serial terminal to connect...
    while(1) {
        blue_led = 0;
        wait(0.2);
        blue_led = 1;
        wait(0.2);
    }
}

USBDevice/USBHAL_KL25Z.cpp/shortlog@9506bdafbf94: not found in manifest