0.6.1: bug fixes and reporting stream-related information

From the changelog:

Added

• Debug number of total and unreleased events in a stream.
• Debug the total number of non-garbage-collected streams across all devices.
• Verifies that compilation options fit in a set of characters: alphanumeric and a few interpunction.

Fixed

• Docu-comment typo.
• The flags cu_event_wait_external and cu_event_wait_default were switched around for record ?external_ and wait ?external_ event functions.
• Don't destroy released (destroyed) events in Delimited_event.synchronize.