This change allows more complex scope boundaries, including loosening
edges a bit to include related resources of HTML pages (which makes
for more complete archives if desired).

The native Go implementation of LevelDB.

The queuing code now performs proper lease accounting, and it will not
return a URL twice if the page load is slow.

The WARC-Date fields now are UTC times in proper ISO-8601 format. This
makes pywb and other tools happy.

Now generates well-formed, indexable WARC files.