This flushes the log when the previous `Append()` call was too long ago.
Note that this doesn't flush after X seconds of silence; a call to
`Append()` or `Flush()` still has to happen in order to do the flushing.
Some parts of Flamenco had a Command consist of "name + settings", and
other parts used "type + parameters" (with the same semantics). This is
now unified to "name + parameters".
