use startup_32 as entry to system
use SETUP_LEN macro in setup
use movl %eax, %cr0 instead of lmsw
successfully invoked c program
rearranged folder
successfully invoked asm in c
reset idt and gdt in boot/head.S
can be debugged with gdb
modified .gitignore
modified Makefile to make and remove tmp_dir automatically
enable A20, disable 8259 interrupts in boot/setup.S
blank screen to white
add window init