remove misleading comment about thin_dump from thin_check man page
Move source into separate sub directories.
Add persistent_data/lock_tracker for more sanity checking.
Add superblock_lock method to lock_tracker.
make lock_tracker throw if the superblock is unlocked while other locks are still held.
block_t and cache_t fully operational again.
A big raft of changes to the unit-tests
Remove the typedef block_ptr and change code to use block::ptr instead
remove space_map_t
Test space_map_core.
rename space_map_disk_t -> space_map_t
Test space_map_transactional
Change the signature of the space_map->new_block() method, introducing
a span_iterator abstraction.

Rename sm_transactional -> sm_careful_alloc.  Still not happy with the name.

Fix failing test.
test the recursive space map
move space maps to their own sub directory
whitespace
Fix a transaction manager test
rename run_list -> span
array data structure wip
Introduce persistent-data/data-structures/