Version Control With Subversion Source

* svnadmin's --config-dir, --deltas, --fs-type, and --wait

* svnlook's --diff-copy-from, --extensions, --full-paths, --limit,
--non-recursive, --verbose, and --xml

Also, flesh out the documentation for svn's --extensions option for
completeness and correctness.

Finally, finish the work of replacing statically listed subcommand
options with xref's to their descriptions.