feat: Add an Elm module

[m0nhawk]

Description

• Add an Elm module if it detects one of elm.json, elm-package.json, elm-stuff directory or *.elm files.

Motivation and Context

Closes #873

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Screenshots (if appropriate):

How Has This Been Tested?

• I have tested using MacOS
• I have tested using Linux
• I have tested using Windows

Checklist:

• I have updated the documentation accordingly.
• I have updated the tests accordingly.

[m0nhawk]

I have tested this on macOS (screenshot), Linux (latest Fedora) and Windows.

Unfortunately, the ghaction-chocolatey doesn't export variables nicely (I believe it's similar I had with Haskell Support in #546) and it fails to run elm on Windows in Github Actions.

[andytom]

Have a few minor corrections for the docs but in general LGTM, I'm not an Elm user so unable to test locally.

[m0nhawk]

@andytom Thank you. Somehow I missed few lines to fix.

[jonstodle]

An "elm" entry is missing in src/configs/starship_root.rs.

[matchai]

Since this module is a new addition, it would be best if we started using the new mocking functionality introduced in #768, rather than adding a new test dependency.

We've gone ahead and migrated the Node tests to use the mocking mechanism in #867, if you'd like to use it as an example.

[m0nhawk]

@matchai I made the necessary changes to implement new tests (at least the tests are passing for this module).

[matchai]

Looks good to me! 👍
Thank you for taking the time to update the tests.

[matchai]

@all-contributors Please add @m0nhawk for code, docs, and test. 🎉

[allcontributors]

@matchai

I've put up a pull request to add @m0nhawk! 🎉