[ot][spam][crazy] crazylog: append-only random-access data

[Undiscussed Horrific Abuse, One Victim of Many]

it seems it would make sense to give the flush regions and the writes
a common base class of being a node in a linked list.

i think there are also some parts that could optionally be removed or
simplified, since writes are a special thing used only in the latest
flush, they don't need to have chunkregions.