Regenerate thumbnail if file is uploaded again

Thumbnail creation notification is now optional.

v0.3.4

Don't create PubSub topic with create_topic()

Use PubSub to inform when the job is done

v0.3.0

Bump version 0.3.0

v0.2.0

Let watch all over the bucket

v0.1.5

Write metadata

v0.1.4

Fix getting version

v0.1.3: Make thumbnail public

Also fix retrieving version