Add undefined behavior sanitizer. Fixes #49.
Add undefined behavior sanitizer. Fixes #49.

Enable the undefined behavior sanitizer on Unix systems in debug
mode. The simplicity of the code takes into account the fact that
only g++ and clang++ can compile the library. g++ ubsan detects a
few false positives with lambdas, and clang++'s one finds some UB
in libstdc++.

Morwenn/cpp-sort,Morwenn/cpp-sort,Morwenn/cpp-sort,Morwenn/cpp-sort