Where can I find documentation for standard library modules
that are binaries rather than Ruby code?  For example, 
Ruby comes with readline support, but as far as I can tell
no documentation.  And since it's a .so I can't easily just look
at the source (although I can always unpack the Ruby source distribution
and dig that way).  I didn't see anything about it in my copy of the Pickaxe,
either.

Anyway, my specific question is this: how do I configure the readline history?
If I just do this:

	ruby -rreadline -e 'Readline.readline; Readline.readline'

I have full editing capability on the input line, but no history;
on the second one, I can't move up to the value I entered the
first time.  But the same code executed in irb gives me access to
the history (shared with the lines entered into irb itself).

-Mark