Added full dir list and rudimentary block allocator

In writing the initial allocator, I ran into the rather
difficult problem of trying to iterate through the entire
filesystem cheaply and with only constant memory consumption
(which prohibits recursive functions).

The solution was to simply thread all directory blocks onto a
massive linked-list that spans the entire filesystem.

With the linked-list it was easy to create a traverse function
for all blocks in use on the filesystem (which has potential
for other utility), and add the rudimentary block allocator
using a bit-vector.

While the linked-list may add complexity (especially where
needing to maintain atomic operations), the linked-list helps
simplify what is currently the most expensive operation in
the filesystem, with no cost to space (the linked-list can
reuse the pointers used for chained directory blocks).

Author: geky

Makefile

@@ -31,7 +31,7 @@ size: $(OBJ)
 	$(SIZE) -t $^
 
 .SUFFIXES:
-test: $(TEST)
+test: test_format test_dirs test_files test_alloc
 test_%: tests/test_%.sh
 	./$<