signal.alarm() -> threading.Timer()

[matroskin8]

This pr fixes #10

[matroskin8]

@seemethere
Ok, i see - it's a weird patch. But how about to remove sending signal at all ? %)
How do you think how many seconds lasts this call

from time import sleep

import retry


def foo():
    sleep(5)
    assert False


retry.retry(interval=0, timeout=1)(foo)()

Damn - 45 seconds

I chose retry.it among others, i like it's "success" in arguments. I got addicted to retry.it in my code.. But sigalarm limits me to replace every old home-brew retry-like fragments to retry.it.
Just say do you want to do something - discuss, say NO or so ?