Skeleton for raft
Move srand call, seed from pid
Add raft.capnp
Make u2_reck_plan push to roe
WIP Make _lo_work rafty

Carts are now batches of events waiting to be or just recently
persisted. _lo_work calls u2_reck_kick on the last batch of events,
removes every batch that's been through Raft, and then prepares the next
batch.

TODO make _lo_punk et al stick things on roe

TODO move disk persistence to raft.c

TODO raft_push: lo_open / mark / lo_shut
WIP rafty loop.c

_lo_save() sticks events on roe for processing in later calls to
_lo_work().
WIP raft single instance

Shove all our disk stuff crudely into raft.c.
Trivial fixups
WIP Move lug_u to u2_raft
More loop -> raft, add u2_raft_boot
New event loop working, super rough cut
Write term and log type, in preparation for raft
Splinter disk persistence and reck stuff back out