Add support for partials

[kizu]

We should add a way to split the slides into several files and then recombine them into one.

[nerevar]

added for notifications

[nerevar]

ping. When can you fix it?

[kizu]

@nerevar I want to refactor a lot of things here, so it would be easy to add proper partials, however, if you really need it, I could do a quick implementation that would work for your case, but it would be trashed when I'll get to the refactoring. When do you need this feature?

[nerevar]

@kizu Hope to see all code reviewed, refactored and ready to use to the beginning of November... Is it possible to do it?