Minor changes. Reading from disk doesn't work (qemu-kvm)

*The print_string_real_mode now adds a newline before it
*The INT 0x13 routine fails using quemu as virtualization platform
*Added new targets to the Makefile (kernel and test)
Fixed the generated image. Bootstraps the kernel.

*The image didn't work previously with the INT 0x13 routine
because the image generated was too small (592 after adding the kernel),
now it uses dd to add 1MB of zeros at the end of the image
*The kernel is successfuly loaded into memory and called. The 'K' char
is printed on the screen
*The bootloader is usable and finished