expanding one tab to 4 spaces
Add .gitignore to ignore binary and tag files.
define system call constants.
Refine MACRO name.
Replace system call numbers with macro constants.
Move "Task Control Block" releated codes from kernrl.c to TCB.h
	new file:   TCB.h
    struct user_thread_stack and struct task_control_block from kernel.c
Abbreviate "task_control_block" to "TCB"
Ignore *.swp file.
ladsh1.in for the input to ladsh1
Abbreviate "task_control_block" to "TCB"
Replace task status macros with enum TASK_STATUS.
Move TCB.h to proc.h, which contains process controling related macros, structs, and enums.
Seperate some syscall C implemntations from kernel.c to syscall.c