#15 RIS-RISX autodetection

[Marc Herbert]

Since it's technically easy to guess if a file is RIS or RISX, without ambiguity, the "addref" command could do that when no explicit input format is specified.

[Markus Hoenicka]

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While it is not hard to distinguish the file types
(med2ris.pl does just this, for example), it is quite tricky
to fit it into the current way refdbc handles input. XML
data are sent chunk-wise as expat can handle this. RIS data
are sent one dataset at a time as the RIS parser can handle
only full datasets at the moment. Therefore the data are
read by different functions from the input stream. While I
see that this feature would be nice to have, the required
changes are larger than I currently want to handle. I've
lowered the priority but will leave this request open.