New Language: C3 (#5086)

Related to: https://github.com/compiler-explorer/infra/pull/1017

C3 is a system programming language based on C. It is an evolution of C
enabling the same paradigms and retaining the same syntax as far as
possible.

Design Principles:
Procedural "get things done"-type of language.
Try to stay close to C - only change what's really necessary.
C ABI compatibility and excellent C integration.
Learning C3 should be easy for a C programmer.
Data is inert.
Avoid "big ideas" & the "more is better" fallacy.
Introduce some higher level conveniences where the value is great.

You can try it out live on its tutorial website:
https://www.learn-c3.org
Source code: https://github.com/c3lang/c3c

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Co-authored-by: Rubén Rincón Blanco <git@rinconblanco.es>

CONTRIBUTORS.md

@@ -129,3 +129,4 @@ From oldest to newest contributor, we would like to thank:
 - [Madhur Chauhan](https://github.com/madhur4127)
 - [VoltrexKeyva](https://github.com/VoltrexKeyva)
 - [Johel Ernesto Guerrero Peña](https://github.com/JohelEGP)
+- [Ali](https://github.com/aliaegik)