Augment ScriptInfo's Javadoc

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
ScriptInfo: support implicit script input parameters

It is sometimes important to support script engine-specific settings,
e.g.  in the ImageJ 1.x macro engine, we need to be able to set the
macro options because the SciJava script service runs scripts on
threads different from the caller's.

This change introduces a special class of settings: input map
entries whose key starts with a dot (e.g. .macroOptions) are considered
implicit, i.e.  no errors about "no such parameter" will be produced.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>