RFC: Optional meaningful return values on write/close in the streaming interface

[Ævar Arnfjörð Bjarmason]

I have a WIP proposal for adding optional return values to the
write/close methods specified for the streaming interface here:

https://github.com/plack/psgi-specs/wiki/Proposal:-Return-values-for-PSGI-streaming-functions

Comments welcome, I already have code that works around this running
on production systems, but I think it's a something that would be
worth adding to the spec, comments/improvements and other feedback
welcome either here or at
https://github.com/plack/psgi-specs/issues/27.