Add two extra exports

[amesgen]

Description of the change
Thanks for these useful bindings! This is a small ad-hoc PR to add support for two missing options:

• navigateWithinSoftTabs is mentioned on https://github.com/ajaxorg/ace/wiki/Configuring-Ace
• placeholder is for some reason not mentioned there, but it is in the API docs.

---

Checklist:

• Added the change to the changelog's "Unreleased" section with a link to this PR and your username
• Linked any existing issues or proposals that this pull request should close
• Updated or added relevant documentation in the README and/or documentation directory
• Added a test for the contribution (if applicable)

[amesgen]

CI failure looks unrelated, should I try to fix it in this PR?

[garyb]

Ah yeah, if you could that'd be great - the package set just needs updating to a value that actually exists.

So prepare-0.15 -> psc-0.15.4-20230105 in

purescript-ace/packages.dhall

Line 2 in f5ef6a8

https://raw.githubusercontent.com/purescript/package-sets/prepare-0.15/src/packages.dhall

would do the trick!

[garyb]

Thanks!

[amesgen]

Thanks, published: purescript/registry#150