WFDB-compatible directory/URL structure

[bemoody]

URLs such as 'https://physionet.org/physiobank/database/mitdb/100.hea'
must be maintained.

Likewise 'https://physionet.org/physiobank/database/wfdbcal',
'https://physionet.org/physiobank/database/DBS' and possibly other
things.

/physiobank/database/ could in theory be a symlink to some other
location if you think that's prettier. But, to make lightwave (and
future things) work in a sane way, we do actually want to have a
single directory containing

DBS
mitdb/RECORDS
mitdb/100.hea
mitdb/100.dat
mimic3wdb/RECORDS
mimic3wdb/30/3000003/3000003_0008.hea

and so forth...

[bemoody]

It's also worth mentioning that for security, the main PhysioBank
directory must never contain data for unpublished projects, even if
restricted by filesystem or webserver permissions.

We want to know that if sandboxed-lightwave (or anything else: rsync
server, sftp server, bittorrent server, ...) chroots into that
directory, it will be incapable of accessing any private data.

I doubt this will ever be an issue but I figured it was worth pointing
out.