Return number of buffer entries on write to buffer

When writing an entry to an ets_buffer return the current num_entries count rather than just true. This allows actions on particular values. Also this Pull Request adds a high water mark for the total number of entries in an ets_buffer and the ability to clear it so that the accumulated size can be monitored on a periodic basis. It also adds timestamps for each entry so that when reading from the buffer the resting latency of an entry can be determined.