Adapt code to C++17 standards

[parham-k]

btllib is implemented with C++11 standards. Compiling with C++17 (e.g., for argparse used in randseq) causes clang-tidy to raise errors. Currently, we compile randseq with C++17 and the rest of btllib with C++11, but it'd be better if we refactor the library with C++17 standards in mind.