Remove Expr::new

[Huliiiiii]

#897 (comment)

I'm considering removing Expr::new, since we already have Expr::from.
As @Expurple mentioned here, I checked my codebase and found that using Expr::from makes the intent clearer. Moreover, accepting Into in the new method is not idiomatic in Rust.

[tyt2y3]

I think we should leave it here for compatiblity , but we can deprecate it.

[Expurple]

Agree with @tyt2y3. I'd include only the most necessary (most beneficial and unblocking) breaking changes in 1.0.0. It's already a big release. Similar to the other minor warts, I'd deprecate Expr::new later in 1.x and remove it in 2.0.0.

It would be nice to track these future deprecations somewhere. So far, I've usually put the word "legacy" somewhere in the doc-comment. Which is good to have anyway, so that no one wonders why the wart is there and whether it actually has any hidden meaning/intention

[Huliiiiii]

But this was added in 1.0.0-rc.1 (#889). I think this does not affect compatibility.

[Expurple]

Ah, forgot about that