Add a severity property to warnings

[fraxken]

As time goes by, I think that not all warnings are equivalent.

I want to add a new severity property for each warning:

• Information (For things not related to security, with valid values or a lot of false positive).
• Warning (the default).
• Critical (Implies malicious code or intent).

Maybe the way we call them is not right ? Maybe we should call warning "Alarm" ?

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I will classify the existing warnings this way:

• Information: parsing-error, encoded-literal
• Warning: ALL OTHERS
• Critical: obfuscated-code

[Mathieuka]

I'm in ☝🏼 🙂