Custom metadata provider

[Rod Widdowson]

> That would work if the goal is to feed an octet stream, but I would expect
a
> database approach is possibly more about avoiding the XML entirely.

Good point.  In that case one might want the thing to implement
BatchMetadataResolver (and hence extend AbstractReloadingMetadataResolver)
but rather DynamicMetadataResolver (and hence extend
AbstractDynamicMetadataResolver).

Now that would be very nice.  Minimal in memory footprint...

R