Update the package structure for Nimble

[WeebNetsu]

After installing this with Nimble we get this warning:

Warning: Package 'karax' has an incorrect structure. It should contain a single directory hierarchy for source files, named 'karax', but file 'widgets.nim' is in a directory named 'experiments/trello' instead. This will be an error in the future.

Hint: If 'experiments/trello' contains source files for building 'karax', rename it to 'karax'. Otherwise, prevent its installation by adding `skipDirs = @["experiments/trello"]` to the .nimble file.

Seems like this will become an error in the future

OS: Arch Linux Nim: 1.6.0 Nimble: 0.13.1