Update documentation.
Add tamer::fd::open_limit().

Return and/or set the limit on the number of open files.
Use tamer::fd::open_limit to improve test on Mac OS X.
Add tamer::fd::shutdown(int how).
Improve error behavior of tamer::fd::make_[non]blocking.
testie: Correctly handle alternates in {{}} regex.
t14 test: Make it work on Mac OS X.

Unlike Linux, Mac does sometimes send an early close notification
on shutdown().