Add Pyret

[BNAndras]

Please complete the following information about the language:

• Name: Pyret
• Website: https://pyret.org/
• Language Version: Summer 2021

The following are optional, but will help us add the language:

• Test Frameworks:
  Built-in, see docs here
• How to install:
  Available as npm package at https://www.npmjs.com/package/pyret-npm
• How to compile/run:
  pyret file.arr starts a compile server that compiles file.arr to a JS file and then runs it with node.
• Any comments:
  The language is currently in use to teach introductory computer science in American high schools and college. It features strongly in A Data-Centric Introduction to Computing, a free online textbook, and has a gentle learning curve with descriptive errors.

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