javadoc --release should auto-link to JDK docs

The javadoc `--release` option could (should?) auto-link to the standard JDK docs for that release, maybe using a configurable table of there equivalent of `-link` options for each of the releases.

We should consider if there needs to be a way to disable the feature. If the table of links is configurable, maybe an empty table is enough.

Note ... handling JDK 9, 10 may be a bit tricky because they precede using module directories; since those releases are no longer supported, it may be that we do not support this feature for those releases, if it is difficult to do so.