Use transparent representation to allow casts

[Plecra]

A repr(transparent) annotation would allow users to (soundly) cast pointers to Ts to UniCase<T>s. This is handy when you can't trivially dereference the pointer, which can come up in generic code.

• Also mentioned here: Support Borrow trait so UniCase can be used as a hashmap key #22 (comment)
• This should be a fairly trivial change. LMK if you want a PR 😃

[ijackson]

This is not trivial, sadly. A UniCase<T> actually contains an enum, so that it can represent whether the contained object is pure-ascii or not, for optimisation purposes. So a UniCase<T> cannot be cast back and forth with a T since the representation is actually different.

[Plecra]

Ahw, that's a shame. Nevermind then

[ijackson]

But see #49

[aQaTL]

How about adding repr(transparent) to unicase::Ascii then?
I understand it could seem unintuitive to have it on Ascii, but not on Unicase, but it would be useful for people that want it to use it as a HashMap key and only care about ascii strings. At least until #49 is merged.