Add `with-struct-timeval'

Signed-off-by: Julien Danjou <julien@danjou.info>
Add low-level fd handling

This adds handling of low-level file descriptor polling for read, write and
timeout.

Signed-off-by: Julien Danjou <julien@danjou.info>
Merge pull request #61 from jd/master

Low-level fd listening support