Custom rom path tokens

[d0k3]

Is your feature request related to a problem?

I personally like to have some sort of custom sorting, f.e. I don't want to mix aftermarket rom dumps with "regular" ones. I could use the dat file names as folder names, but I'd actually prefer my old, custom ones.

Describe the solution you'd like

I'd prefer a way of creating my own {token}, or some rules which would handle which rom dumps go where. For example: [...] Atari - Atari 2600 (Aftermarket) -> a2600am Bandai - WonderSwan -> ws Bandai - WonderSwan -> wsc [...]

Additional context

igir already provides tokens such as {es} or {batocera} to match the folder structure used by popular tools. There is also the --dir-mirror option, but that is not flexible enough to handle properly adding new files to the collections.