Add the Curry programming language

[fwcd]

Description

This PR adds the functional logic language Curry, as proposed in #795.

See also:

• https://en.wikipedia.org/wiki/Curry_(programming_language)

Checklist:

• I am adding a new language.
  • The extension of the new language is used in hundreds of repositories on GitHub.com.
    • Search results for each extension:
      • search results for .curry
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • Prelude, the core of Curry's standard library
      • Data.Nat, a representation of Peano numbers in Curry, showcasing e.g. free variables
    • Sample license(s):
      • BSD-3: https://git.ps.informatik.uni-kiel.de/curry/curry-libs/-/blob/master/LICENSE
      • BSD-3: https://git.ps.informatik.uni-kiel.de/curry-packages/peano/-/blob/master/LICENSE
  • I have included a syntax highlighting grammar:
    • Lightshow link
    • Grammar link
  • I have updated the heuristics to distinguish my language from others using the same extension.
    • not necessary, since no other languages use .curry

Color

I chose the color #531242 for Curry as a blend of blue and red, the colors of the official logo. Additionally, the color is similar to Haskell's color #5e5086 and Prolog's color #74283c, which provides a nice analogy, considering how Curry combines Haskell's syntax with many of Prolog's features.

[Alhadis]

Bit light on usage, I'm afraid. Of the 4,437 files indexed by GitHub, I managed to harvest 4,402 of them, yielding only 56 repositories among 46 users. Since this falls far below the minimum usage criteria, I didn't bother downloading the results to pick out false matches, so the actual number of relevant users might be even less than this.

We can monitor .curry usage by adding it to #4219. Once the language reaches sufficient popularity, we can revisit this.

[lildude]

Please can you address the conflicts.

Once this is good to go, I'll approve this based on the temporary requirements detailed in #5756

[fwcd]

Sure, I've rebased the branch on the current master.