Support arbitrary expression for `#[builder(default = ...)]`

[bew]

Hello!

I initially tried out the typed-builder crate but realized I needed runtime checks.
While migrating to derive_builder I noticed the syntax for default is less ergonomic.

With typed-builder I could do: #[builder(default = "foo".into())]
But with derive_builder I need to wrap the fn in a string: #[builder(default = r#""foo".into()"#)] which is much less ergonomic, and in an editor I can't do actions like 'go-to-definition'.

So here I am, asking to support that ;)

[TedDriggs]

I've put up a PR for this, though I haven't had enough time to fully test it, and I was seeing some weird behavior from rust-analyzer in vscode after I made the change.

[bew]

Hello again, thanks a lot for the impl it looks great and simple!

Do you have any plans to make a release some time 'soon'(-ish) ?

[TedDriggs]

Yes, I will do one this week when I have time.

[TedDriggs]

@bew I have now published 0.20.2 with this change.