Add FS usedSize() and totalSize()

teensy/FS.h

 	virtual bool rename(const char *oldfilepath, const char *newfilepath);
 	virtual bool remove(const char *filepath);
 	virtual bool rmdir(const char *filepath);
+	virtual uint64_t usedSize();
+	virtual uint64_t totalSize();
 };
 
 

teensy3/FS.h

 	virtual bool rename(const char *oldfilepath, const char *newfilepath);
 	virtual bool remove(const char *filepath);
 	virtual bool rmdir(const char *filepath);
+	virtual uint64_t usedSize();
+	virtual uint64_t totalSize();
 };
 
 

teensy4/FS.h

 	virtual bool rename(const char *oldfilepath, const char *newfilepath);
 	virtual bool remove(const char *filepath);
 	virtual bool rmdir(const char *filepath);
+	virtual uint64_t usedSize();
+	virtual uint64_t totalSize();
 };