[WIP] Add Elm

[Gauteab]

What

Adds support for the Elm programming language

Checklist

• [ x ] Recorded tests for the new language
• [ x ] Used "change" / "clear" instead of "take" for selection tests to make recorded tests easier to read
• [ x ] Added a few specific tests that use "chuck" instead of "change" to test removal behaviour when it's interesting, especially:
  • [ x ] "chuck arg" with single argument in list
  • [ x ] "chuck arg" with multiple arguments in list
  • [ x ] "chuck item" with single argument in list
  • [ x ] "chuck item" with multiple arguments in list
• [ ] Added a test for "change round" inside a string, eg "hello (there)"
• [ x ] Supported "type" both for type annotations (eg foo: string) and declarations (eg interface Foo {}) (and added tests for this behaviour 😊)
• [ x ] Supported "item" both for map pairs and list entries (with tests of course)

Currently not working

• Strings
• "take every arg"

[pokey]

Oh yeah also lmk if you want help with getting strings to work, and with getting "change round" to work inside strings

[pokey]

Closing this one as it looks like it's been stalled for a bit. Filed #1088 to track. Feel free to re-open if you get a chance to hack on it again 😊