Retroachievements Multiset

[poketrainernoxx-oss]

Please allow emuhawk to unlock achievements for subset/bonus sets in retroachievements.

Explanation is here: https://docs.retroachievements.org/guidelines/content/subsets.html

From Reddit:

<CPP> It probably won't happen for a while, and even then, BizHawk updates occur at a glacial pace, so [...] you wouldn't be able to use it for a long while.
<Yoshi> Are there technical barriers or only time?
<CPP> Only time really.