Automatic series recognition can generate false positives too easily
when the default series configuration is flexible enough to handle
common cases.  Avoid false positives by requiring an explicit syntax to
activate series recognition.  Choose the syntax DATA{<name>,:} to be
short, simple, and look like a vertical ellipsis.

This allows us to improve the default series match configuration.  Allow
series references to contain one of the numbered file names.  Allow '-'
as a separator in addition to '.' and '_'.  Document what the default
configuration matches.  Also provide more options to configure series
<name> parsing.