toml: support inline tables in arrays

[sersorrel]

Syntax like this is valid TOML:

list = [ { z = 1 } ]

but currently it gets incorrectly rejected by Rouge:

I believe this change fixes that without introducing any obvious side-effects.

As a side-note: since 1bdd9486297f37bb95c298eb68409666bd9906fc, I think the special case for ident = { in :basic is probably no longer necessary, but I'm not confident enough in that to actually remove it right now. I also think having the ident = case in :content is incorrect, and that should be in :inline instead (or in some mixin that can be shared by :root and :inline) – currently, things like x = [ y = 2 ] are accepted despite being invalid TOML, and I believe that rule is the reason for that.