Fix value of "received options" in error message

[c4710n]

This PR aims to close #127.

• In order to get the original opts when composing the error message, I extended the second argument of reduce_options/2.
• There is also a trivial modification that unifies the function signatures of validate_unknown_options/2 and validate_options/2.

I am not very confident in the elegance of this code; comments are welcome, and I am happy to make revisions.

[coveralls]

Pull Request Test Coverage Report for Build d725b0bd19d95a07db55f812c3e065ecb7105911-PR-128

Details

• 8 of 8 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 93.0%

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Totals
Change from base Build a3acae8e316935696d50e59140454f9cc20402b6:	0.0%
Covered Lines:	279
Relevant Lines:	300

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💛 - Coveralls

[whatyouhide]

Thank you @c4710n 💟

[c4710n]

My pleasure!