shell / ioManager: don't allow backspace when input buffer is empty

fix issue #3: crash when running an unknown program

xhci: show device information using usb strings

xhci: print basic usb device information

xhci: clean up slot initialization

xhci: send get device information command to attached usb devices

xhci: configure endpoint

xhci: send address device command

fix weird problems with getPhysicalAddress system call

xhci: request a slot for each activated port

enable xhci ports with a connection

fix issue with printing where the first message would not get printed

create async xhci command function using events

trigger interrupts from xhci controller

fix problem where page fault happens because not the whole string is mapped in a insertString system call

refactor syscall.c

fix issue vga driver: newline doesn't move cursor #2

use sleep function for xhci driver waiting for the controller to start

add sleep function to PIT driver

add system time readout

add basic PIT timer outline

receive xhci events

try initializing xhci hub

fix issue #1: ELF files not loaded correctly

print out xhci port info

refactor usb driver to use an internal memory structure

allocate scratchpad buffers whenever implemented

add system call to retrieve the physical location of a virutal address

initialize XHCI controller and correctly list anvailable slots

add screenshot to README