file based save states, and improved file structure

include/cart.h

@@ -63,6 +63,8 @@ bool cart_load(char *cart);
 
 rom_header *get_rom_header();
 
+cart_context *cart_get_context();
+
 u8 cart_read(u16 address);
 void cart_write(u16 address, u8 value);
 

include/state.h

@@ -22,4 +22,7 @@ typedef struct {
 } save_state;
 
 void state_save(save_state*);
-void state_load(const save_state*);
+void state_load(const save_state*);
+
+void state_save_file(u8 slot);
+void state_load_file(u8 slot);