Document the behavior of "User Shutdown" queue sink input

[Ethan Stern]

Add documentation to LVQueueSink that explains the behavior of “User Shutdown” option

[[e-mail]]

Added buffered log sink and test coverage, resolved issue #1, resolved issue #2, resolved issue #3, resolved issue #4, GPackage version 0.7.0

→ <<cset d4a062399a59>>