v1.2.2: Bug fix in `Blrt` and C++ refactor

 - Bug fix for `Blrt::Bootstrap` by sampling correctly from the prior,
   previously, it sampled from a uniform prior which is incorrect. This
   affect results from models with largely varying priors
 - Modernise C++ code, such as using containers, iterators, `const`,
   `std::size_t`, templates, ...etc. This will improve maintainability
   and, in certain cases, performance
 - Remove underflow detection as this was implemented incorrectly and
   never used