SRFI 41, revisited

[Chris K. Jester-Young]

It's been over half a year since I last wrote about SRFI 41; two whole
releases have happened since then. I'm pretty sure I don't want to wait
for another. ;-)

Thanks to Andy and Ludovic for all the feedback last time; I think I've
implemented all the feedback, so let's get this thing across the finish
line! I just updated the srfi-41 branch with a merge of v2.0.6, and ran
the tests (which passed with no changes to the code).

So, a final review would be highly appreciated.

One thing that is still missing is the documentation. I believe Ludovic
mentioned that this can be lifted straight from the SRFI specification
if need be. (I do hope to write something more original, even if only as
a later thing. But let's not let that hold up making srfi-41 available!)

Cheers,
Chris.