PR: Add STIL to the list of supported languages

[andfoy]

Description of Changes

This PR adds a temporary hack to detect languages based on their extensions, and adds STIL as a supported language (required by TDK).

cc @nerohmot

• Wrote at least one-line docstrings (for any new functions)
• Added unit test(s) covering the changes (if testable)

• Included a screenshot or animation (if affecting the UI, see Licecap)

Issue(s) Resolved

Fixes #

Affirmation

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[ccordoba12]

Thanks @andfoy, looks good to me.