Add the initial core components of the LSM implementation to be able to
read the root inode:
- bio.c: read big block regions
- seg.c: cache logical segments
- ring.c: read the manifest from storage
- manifest.c: organize segments into an LSM
- kvec.c: work with arbitrary memory vectors
- item.c: cache fs metadata items read from segments
Signed-off-by: Zach Brown <zab@versity.com>