Add PartialEq/Eq impls to proc_macro::{Spacing, Delimiter}

[LukasKalbertodt]

I don't see a reason why those two types shouldn't be tested for equality. But I hardly know anything about proc macros, so I'm probably wrong :)

[rust-highfive]

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[nikomatsakis]

I agree these ought to be comparable for equality.

[nikomatsakis]

@bors r+

cc @nrc @jseyfried @alexcrichton -- you all are as close to owners of the proc macro stuff as I can think of just now, so probably ought to be aware, but this seems harmless enough.

[bors]

📌 Commit 4ba242b has been approved by nikomatsakis

[bors]

⌛ Testing commit 4ba242b with merge 7e5578d...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: nikomatsakis
Pushing 7e5578d to master...