Feature/signature checking

[fabulousduck]

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[fabulousduck]

I opted to not add a test for this as it is a tiny change and it tested this manually.
@meltingice whats your opinion on straight up throwing an error ?
Do you prefer this method, or would you rather it not throw one and return an error string or something like that ?

this solves #90

[fabulousduck]

#96 changed the package which i also did by trying out tests with chai in this branch. Fixed now and can be merged without conflicts.