Pass though opts parameter to metadata hypertrie

[fsteff]

implements #301 using the opts.db namespace

But for hidden files to actually work as expected, mountable-hypertrie#9 has to be solved - either in hyperdrive or there.

[fsteff]

The newest commit uses my fork of mountable-hypertrie. Obviously this has to be changed back, but for demonstration purposes it works.

[mafintosh]

Old major, thanks tho!