TTL of data cleaned inside Bot API optimize_memory (enhancement of #40)

[cavallium]

If possible, add an hardcoded TTL of few seconds to clean only data older than a few minutes,
to avoid missing updates or missing data in new updates.

This shouldn't be configurable since this TTL, of few seconds, is made only to prevent this kind of problems, and not to ensure long-term data presence after optimize_memory.