Bootloader: Split bootloader into multiple files

This cleans up the code since bootloader is starting to near 1k lines

bootloader/command_line.S

@@ -0,0 +1,69 @@
+.code16
+
+.section .stage2
+
+# fills command line buffer
+# NO REGISTERS SAVED
+.global read_user_command_line
+read_user_command_line:
+	movw $command_line_enter_msg, %si
+	call puts
+
+	movw $command_line_buffer, %di
+
+ .read_user_command_line_loop:
+	call getc
+
+	cmpb $'\b', %al
+	je .read_user_command_line_backspace
+
+	# Not sure if some BIOSes return '\n' as enter, but check it just in case
+	cmpb $'\r', %al
+	je .read_user_command_line_done
+	cmpb $'\n', %al
+	je .read_user_command_line_done
+
+	call isprint
+	testb %al, %al
+	jnz .read_user_command_line_loop
+
+	# put byte to buffer
+	movb %al, (%di)
+	incw %di
+
+	# print byte
+	call putc
+
+	jmp .read_user_command_line_loop
+
+ .read_user_command_line_backspace:
+	# don't do anything if at the beginning
+	cmpw $command_line_buffer, %di
+	je .read_user_command_line_loop
+
+	# decrement buffer pointer
+	decw %di
+
+	# erase byte in display
+	call print_backspace
+
+	jmp .read_user_command_line_loop
+
+ .read_user_command_line_done:
+	# null terminate command line
+	movb $0, (%di)
+
+	call print_newline
+
+	ret
+
+
+command_line_enter_msg:
+	.asciz "cmdline: "
+
+
+.section .bss
+
+# 100 character command line
+command_line_buffer:
+	.skip 100