Add support for Lambdapi language (.lp)

[Alidra]

Description

Checklist:

• [x] I am adding a new language.
  • [x] The extension of the new language is used in hundreds of repositories on GitHub.com.
    • Search results for each extension:
      • https://github.com/search?q=NOT+is%3Afork+path%3A*.lp+%2F%28%3F%3A%5E%7C%5Cs%29symbol%28%3F%3A%24%7C%5Cs%29%7C%28%3F%3A%5E%7C%5Cs%29rule%28%3F%3A%24%7C%5Cs%29%2F&type=code
  • [x] I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • https://github.com/Deducteam/lambdapi/blob/master/tests/OK/List.lp
      • https://github.com/Deducteam/lambdapi/blob/master/tests/OK/tutorial.lp
    • Sample license(s): MIT
  • [ ] I have included a syntax highlighting grammar: [URL to grammar repo]
  • [x] I have added a color
    • Hex value: #8027a3
    • Rationale: The color was chosen by the community of users
  • [x] I have updated the heuristics to distinguish my language from others using the same extension.

[Alidra]

See inline comments.

The samples/Lambdapi/List.lp sample is also too big. If it's suppressed in the diff, it's too big for our needs. Please replace it.

Can you please update the search query in the PR template to more accurately identify just this langauge. From a quick look it appears to be matching other languages already correctly identified. You can use regular expressions so I'd recommend using the one you're adding for the heuristic, once you've addressed the problems with it.

I believe all the comments have been addressed. Please let me know if any more changes are required.

[Alidra]

Hi @lildude, Are there any more changes requested to merge this PR?