changed to optimized build by default
several changes in TOOLS::FS - be more explicit, avoid implicit conversion and all join-alike (i.e., +, .join()) lead to a copy-by-value, without changing the original object, although this seems not (perf) optimal, it is easy to use - python inspiried maybe
some comments in fs.cc concerning new features/methods
minor
FS::Path now always copies on path concat operations (join(), +, ...)