Move filesystem code into its own directory

Step one into cleaning up the codebase a little bit.

sw/Makefile

@@ -15,7 +15,7 @@ LISTS=lists
 TESTS=tests
 
 SRCS=$(wildcard *.s) $(wildcard *.c)
-SRCS+=$(wildcard usb/*.c)
+SRCS+=$(wildcard filesystem/*.s) $(wildcard filesystem/*.c)
 OBJS+=$(patsubst %.s,%.o,$(filter %s,$(SRCS)))
 OBJS+=$(patsubst %.c,%.o,$(filter %c,$(SRCS)))
 

sw/exec.c

@@ -2,8 +2,8 @@
 #include <conio.h>
 #include <string.h>
 
-#include "fat.h"
-#include "o65.h"
+#include "filesystem/fat.h"
+#include "filesystem/o65.h"
 
 void exec(char* filename) {
 	o65_header_t* header;

sw/filesystem/fat.c

@@ -1,7 +1,7 @@
 #include <conio.h>
 #include <string.h>
 
-#include "fat.h"
+#include "filesystem/fat.h"
 #include "sd_card.h"
 
 uint8_t fat_buf[512];

sw/main.c

@@ -6,8 +6,7 @@
 #include "uart.h"
 #include "mapper.h"
 #include "sd_card.h"
-#include "fat.h"
-#include "o65.h"
+#include "filesystem/fat.h"
 #include "exec.h"
 
 uint8_t buf[512];