fix cursor issues

[nnyyxxxx]

closes #9

[nnyyxxxx]

before:

after:

[nnyyxxxx]

ready to be merged @adamperkowski

[nnyyxxxx]

ignore the extra space, it is not caused by this PR rather this snippet in interrupts.rs

                            // backspace
                            unsafe {
                                if BUFFER_INDEX > 0 {
                                    BUFFER_INDEX -= 1;
                                    WRITER.lock().decrement_column_position();
                                    print!(" ");
                                    WRITER.lock().decrement_column_position();
                                }
                            }