support checking against leafo's tableshape type object predicates

[jvprat]

Hi,

I'm on the process of writing a library that needs to do type checking for arbitrary values, other than arguments and return values, and I'd like to reuse the type specification syntax from this library.

Would you mind adding a new public function that factors out this functionality? I could work on the task if you're interested. (Or maybe you know a better library for this? I haven't found any)

By the way, thanks for working on this library on the first place! It's very useful :smiley: