Set ffmpeg_timeout to zero by default.

[almarklein]

On an Ubuntu 18.04 VM, I can easily reproduce ffmpeg being killed using this script:

import imageio_ffmpeg
import numpy as np

ims = [np.random.uniform(0, 255, size=(1000, 1000, 3)).astype(np.uint8) for i in range(10)]

w = imageio_ffmpeg.write_frames("/home/almar/Desktop/foo.mp4", (1000, 1000), ffmpeg_timeout=0)
w.send(None)
for i in range(200):
    w.send(ims[i % 10])
    print(i)
w.close()
print("closed")

If we can assume ffmpeg to not hang doing nothing, it would be much better to set the default timeout to zero (i.e. wait until ffmpeg is done). However, we probably want to combine this with proper keyboardinterrupt handling #4.

[almarklein]

cc @djhoese because you're the one adding the timeout parameter