[Kst] Plugin documentation update

[Brisset, Nicolas]

Hi,

I am experimenting with new (at least to me) things with data plugins,
and there are some undocumented features I'd like clarifications about
(an update to KstPlugins in devel-docs/ would be the most appropriate I
guess):
- George once wrote that strings are supported provided that there is
the following C signature:
Plugin(inVectors, inVectorLens, inScalars, outVectors, outVectorLens,
outScalars, const char* inStrings[], char *outStrings[]) if I remember
it right. It would be nice to add it to the doc, which currently says
explicitly that only scalars and vectors of floats are supported ! I
have not come so far as to test it yet, but hopefully it is the doc
that's out of sync.
- how does one provide a "fit" plugin that will show up in the list of
fitting plugins when invoked via RMB->Fit ? Is it the <fit/> keyword in
the intro node of the .xml file ?
- when fitting a function, who generates the label that shows up in the
plot (which by the way seems to have a bug in the way the '.' character
is rendered) ? Can or does the plugin need to provide an output string
for that purpose ? 
- what is the purpose of the floatNonVector type ?

Beyond those concrete questions, I have just had a quick look at
pluginxmlparser.cpp and plugin.cpp it looks like there are plenty of
other features that would need to be explained somewhere...

Thanks,

Nicolas