Clarity in comments in example code
Briefly introduce variadic XSUBs

This serves as a vehicle to point out difference in behavior of many
XSUBs version Perl subs.

They're close, but the rigid argument count checking is a common pitfall.

This change doesn't explain variadic XSUBs completely since it elides any
mention of how to actually inspect the parameters to such a function, and
that required and optional parameters can be mixed. That is on purpose.

The '...' is a very syntactically obvious construct that shouldn't distract
the reader too much at this stage while allowing for instructive discussion
of Perl/XS similarities/interaction.

But explaining the whole argument stack shebang here would be a major
deterrent, so that's deferred until later.
small nitpicks
Explain RETVAL a bit more
Expand on the refcounting

Memory management in XS is tricky. Try to expand on it some.
space out
Merge branch 'tsee/adjustments-additions'