gdss-brick >> gh17 Redesign disk storage: Update API.

Change writeback_to_stable_storage/2 to take a list of wal_entry()
instead of just one wal_entry().
gdss-brick >> gh17 Redesign disk storage: Update API.

Change writeback_to_stable_storage/2 to take a list of wal_entry()
instead of just one wal_entry().
gdss-brick >> gh17 Redesign disk storage: Implement HLog parsers.

Implement brick_hlog_hunk:parse_hunks/1 and parse_hunk_iolist/1.