LRU Least Recently Used caching strategy

[danielweck]

This "TODO" code comment has been present from day-1 in the TypeScript source, still unresolved (time to file an issue!):

r2-streamer-js/src/http/server.ts

Lines 353 to 358 in 6afd236

	public cachePublication(filePath: string, pub: Publication) {
	// TODO: implement LRU caching algorithm? Anything smarter than this will do!
	if (!this.isPublicationCached(filePath)) {
	this.pathPublicationMap[filePath] = pub;
	}
	}

Basically, the cache of ReadiumWebPubManifest models grows indefinitely in the current implementation.