#5 Add argument to contentsChanged()

[Jon Blower]

Requested by Andrew Harrison:
"One thing I reckon might be worth looking at re the
API is the
contentsChanged() of StyxFileChangeListener interface.
I could have done with a contentsChanged(Object change)
or something (or even a
contentsChanged(StyxFileChangeEvent event) type thing).
This object could represent the new content, or
anything really. Given this object, the listener
class (AsynchStyxFile for example) could make decisions
about who to let read the data etc."