Allow use on filename(s) without using stdin

[Adam]

I feel like it would make sense for up filename to be a valid invocation, with it having the same effect as cat filename | up.

[Mateusz Czapliński]

Thanks for the idea! ❤️ For now, I'm kinda more inclined towards leaving the possibility of using the free arguments as a commandline to preload in up... like: up grep "[a-z]", or something similar... this seems potentially more valuable to me currently, as one can still always do cat filename | up as you say, but the other option is not really available in any other way... but I may well still change my opinion at some point still. Let's see what the future brings! :) I'll keep it in mind for sure.

Thanks!