Remove _ from UnpinStruct

[taiki-e]

As UnpinStruct is displayed in the documents, I think it looks better when _ is removed.

Before (https://docs.rs/hyper/0.13.0-alpha.1/hyper/server/index.html):

After:

cc @seanmonstar @LucioFranco

[LucioFranco]

👍 wonder if we could provide the option to name it to a custom name.

[taiki-e]

@LucioFranco

👍 wonder if we could provide the option to name it to a custom name.

Looks like a good idea.

Probably like this?

#[pin_project(unpin_docs = MyUnpinStructName)]
struct Foo<T, U> {
    #[pin]
    pinned: T,
    unpinned: U,
}

(Note: Once rust-lang/rust#48054 is implemented and stabilized, these documents will not be generated, but the options themselves will be maintained for compatibility.)

[LucioFranco]

@taiki-e seems reasonable!

[seanmonstar]

I didn't even realize that it exports a new type. Could it be doc(hidden), or even better, not pub?

[taiki-e]

@seanmonstar
I'm sorry. There is certainly a lack of documentation on this behavior.
This is intended to avoid the issue that cannot know the actual trait implementation bounds of the Unpin implementation from the document of generated code. And a way to opt-out of this was added in #62.

[taiki-e]

I am considering disabling this by default.
This is because the current way is that if the struct is declared in a public module, UnpinStruct is displayed, but if it is declared in a private module, there is a discrepancy that UnpinStruct does not appear in the document.

cc @Aaron1011

[taiki-e]

It should also be a problem that items that are not declared by the user appear in the document without permission.

[taiki-e]

Closing this in favor of #71.