Document flushing of (SQLite) cache

[martinheidegger]

Currently the SQLite cache can be flushed only manually. This behavior (and the apis) needs to be documented!

hyper-dns/cache-sqlite.js

Lines 24 to 42 in 2ab60f4

	async clear () {
	await lru.clear()
	run(Q_CLEAR, {})
	},
	async clearName (name) {
	await lru.clearName(name)
	run(Q_CLEAR_NAME, { name })
	},
	async close () {
	if (db !== null && db.open) {
	db.close()
	db = null
	}
	},
	async flush (timestamp) {
	timestamp = typeof timestamp === 'number' ? timestamp : Date.now()
	await lru.flush(timestamp)
	run(Q_FLUSH, { now: timestamp })
	},