switch from fill to fil

[TeXhackse]

First of all - thanks for maintaining this.

I faced a small issue: When using \hfill inside the frametitle it will not be shifted to the right as the right skip uses 1fill to fill the line.

Not sure if you are aware, but one can easily fix that by using 1fil which actually does the same but is less strong. So if we have 1fill and 1fil the one with 2 “l” will win.

I also saw you did the same vertically and there it's the same as end users usually just use \hfill/\vfill it would be great if you could change that. Hope the explanation is enough to get my points, otherwhise feel free to ask.

[jolars]

Looks great, thanks for the PR! I'll fix the test error and update the \vfill thing separately.