Flake8 fix-up.
Add log.
Don't send eof.
Remove obsolete example.
Remove obsolete.
PetrifyDB => BlockChainStore.
Various DBs.
Fix some test failures.
Got DictStoreSimple working.
Improved tests a bit.
Remove obsolete.
Remove obsolete.
Add block chain locker.
Get petrified writing working.
Remove obsolete test.
Generalize Fetcher.
Get InvCollector working again.
Get TxMempool tests working.
Have TxMempool handle blocks.
Rename TxMempool => Mempool.