Use default type parameter for LocatedSpan

[zakcutner]

Thanks for the help with my previous pull request! I have decided to create another one for something small that has been bugging me for a bit...

When the addition of extra information to LocatedSpan was implemented, a new LocatedSpanEx struct was added which includes an extra property with generic parameter X. Consequently, the original LocatedSpan has become a type alias where X is set to the empty type ().

pub type LocatedSpan<T> = LocatedSpanEx<T, ()>;

However, this is unnecessary as for some time default type parameters have been allowed — see the relevant page in the Rust book for more information on how these can be used. I have simplified the types by renaming LocatedSpanEx back to LocatedSpan and adding a default type of () for the generic X parameter.

pub struct LocatedSpan<T, X = ()> { ... }

It may be important to allow for backwards compatibility so I have recreated LocatedSpanEx as a type alias of LocatedSpan (which can be removed in a future release). I have marked it with a deprecation warning since all uses can now be replaced with LocatedSpan. The remainder of the codebase, including documentation and testcases, has also been updated to simply use LocatedSpan.

#[deprecated(note = "Use LocatedSpan instead which is exactly the same")]
pub type LocatedSpanEx<T, X> = LocatedSpan<T, X>;

Additionally, on an unrelated note, I have fixed a FIXME issue in the testcases whereby the following line was not working.

assert_eq!(BytesSpan::new(b"foobar").compare(b"foo"), CompareResult::Ok);

The issue is that b"foo" has type &[u8; 3] whereas b"foobar" has type &[u8] as it is implicitly casted due to the type signature of ByteSpan::new. The solution is to perform the same treatment to b"foo", which must be done with an explicit cast.

assert_eq!(BytesSpan::new(b"foobar").compare(b"foo" as &[u8]), CompareResult::Ok);

Please let me know if I can clarify anything or if there are any questions or issues with this 😄

[progval]

Excellent!

We're about to release v2.0.0, so you can even drop LocatedSpanEx and add this to the CHANGELOG.md

[zakcutner]

@progval Thanks for responding so fast! These changes are all done now, I've amended the commit as there's probably no need to include the original in the history

[progval]

Thanks!