`educe` uses legacy (^1) version of `syn` crate. about educe

[A1-Triard]

though NestedMeta has been removed

Yep. I tried to research updating syn after I created the issue, but I found that it is difficult to do it without detailed knowledge about educe attributes structure, because it requires to reimplement parsing :-(

So, it would be really cool if you find time to do this job. And without a doubt educe is an amazing thing, either with new or old syn dependency.

[magiclen]

I'm planing to update the syn crate to ^2 (though NestedMeta has been removed).

[magiclen]

Finally, I have completed the migration to Syn ^2. The new version 0.5 has been released.