[WIP] Release notes for 0.73 (#690)

* [WIP] Release notes for `0.73`

Please add your important new features and breaking changes to the release notes by committing to/opening a PR against the `release-notes-0.73` branch. Thank you!

* typo fix (#691)

* Grammar fix

* Update math section

* `mkdir` `--show-created-paths` flag replaced (#701)

* add breaking change for split row (#696)

* Describe `explore`

* Add color_closures and mutable data structure features (#707)

* add breaking change for fetch (#708)

* Update 2022-12-20-nushell-0.73.md

* Update 2022-12-20-nushell-0.73.md

* Update 2022-12-20-nushell-0.73.md

* Update 2022-12-20-nushell-0.73.md

* mkdir breaking change

* `split list` breaking change

* Update 2022-12-20-nushell-0.73.md

* Update 2022-12-20-nushell-0.73.md

* Update 2022-12-20-nushell-0.73.md

Co-authored-by: raccmonteiro <[email protected]>
Co-authored-by: WindSoilder <[email protected]>
Co-authored-by: Reilly Wood <[email protected]>
Co-authored-by: Leon <[email protected]>
Co-authored-by: JT <[email protected]>