feature: allow set each talk in a separate config file

[frankiejol]

This way it will be easier to add some talks in parallel
without conflicting in config.yml

[meis]

Let's put that on hold and discuss it when we have some time.

I'm in favour of having only one config file. I don't see the need add complexity to the build to handle the 'parallell branches' problem. This is because It's never been a problem for me, which does not mean it's not a problem for you.

I'd like to talk about the problem before accepting something like this. Would that work?

[frankiejol]

With the config in one file I had to fix conflicted merges. It would have been easier if I had this feature back then.