Add cpu serial number to EXIF data, not so much because I expect it to
be useful - or because I expect to have *two* Rasperry Pi cameras
someday & the need to distinguish them - but rather because it struck me
as mildly cool and/or interesting to do so.
The url for an image is /images/yyyy-mm-dd/hh-mm.

The actual file names are yyyy-mm-dd_hhmm.jpeg: just different enough to
be annoying, and for no good reason. The inconsistency vexes me, and
must be corrected.
Correct path to exif-reader.js.