enable applying theme by name without knowing its file extension

[mardab]

I just tried using this and despite a bit confusing README, usage is very simple, except for the fact that some themes have .yaml extension and some have .yml extension, and I don't want to remember which one has which, or type whole path by hand, so for myself I just stripped extensions from theme filenames and it works, but for everyone else I believe that it would be nice to be able to change theme without having to specify extension, it seems easy to add this without having to change much else in code.

[tnagorra]

I think a better solution would be using alacritty-colorscheme with fzf

Please check #30