Add the OverPy language

[Zezombye]

Description

Adds support for the OverPy language, a high-level language to make gamemodes in the Overwatch Workshop.

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:
      • https://github.com/search?type=code&q=NOT+is%3Afork+path%3A*.opy+%28rule+OR+define+OR+macro+OR+mainFile+OR+settings%29
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • meipocalypse.opy
      • santa.opy
      • genij.opy
    • Sample license(s):
      • First two are MIT (I wrote these and am accepting to make these available under MIT)
      • genji.opy has no license, I can ask the author to add a license if this is a problem.
  • I have included a syntax highlighting grammar: [URL to grammar repo]
    • https://github.com/Zezombye/overpy-grammar
  • I have added a color
    • Hex value: #78b355
    • Rationale: It is the color of Discord's snake emoji
  • I have updated the heuristics to distinguish my language from others using the same extension.
    • No other language is currently using the .opy extension