store Directory Reference

Files
	backend.hpp
	Storage backend interface: what a session's fills, orders, positions, PnL and kill events are handed to, so they can be queried without replaying the journal.
	reader.hpp
	Query side of a storage backend: what fastmm-pnl and a restarting session read back.
	registry.hpp
	Storage backend registry: name -> factories.
	sqlite_store.hpp
	The SQLite storage backend ([storage] backend = "sqlite"), the one FastMM ships.
	store_thread.hpp
	StoreThread: drains the engine's record ring into a Backend, on its own thread.