Adopted ctz skip-list structure earlier than expected

The primary data structure backing the little fs was planned
to be a little ctz based skip-list for O(logn) lookup and
O(1) append.

Was initially planning to start with a simple linked list of
index blocks, but was having trouble implementing the free-list
on top of the structure. Went ahead and adopted the skip-list
structure since it may have actually been easier.

Makefile

@@ -12,7 +12,7 @@ ASM := $(SRC:.c=.s)
 ifdef DEBUG
 CFLAGS += -O0 -g3
 else
-CFLAGS += -O2
+CFLAGS += -Os
 endif
 ifdef WORD
 CFLAGS += -m$(WORD)