Implements a cassandra-file-compatible segmented log
of "mutations". Handles "batch" and "periodic" mode like
stock version. Also includes "dirty" management for the
interaction log/memtable.
Supports:
* add
* sync/flush
* clear dirty bits (thus discarding segments)
Many more estoric stock functions not yet implemented.
Missing: Storage management. Does not deal with total
size on disk of segments yet. Nor does it have any provisions
for dealing with active buffer bloat should async writes stall.
[avi: adjust for future<>::rescue() removal]
Signed-off-by: Calle Wilund <calle@cloudius-systems.com>
