Consider adding support for Polymega files

[euan-forrester]

According to Tokugamer on the retrostage discord in the polymega-issues channel, there's an app coming soon that will allow users to share save files.

From the press release it might just be save states though: https://polymega.com/blogs/system-software-updates/introducing-polymega-app

Once the app comes out, we should take a look and see if it's save states or in-game saves and if it's in-game saves get a few example files (one for each system) and see if they need any conversion.

Polymega firmware release notes: https://polymega.com/pages/changelog