reviewed new/delete use; fixes after valgrind runs
added CharMap template arg to radix_sort, solving the problems of estimating the data types; added notes on memory+cpu requirements
initial implementation of RADIX sort - needs polishing
minor comment updates in ToDo
added more test cases for CompressedSparseTrie; added comments to greedy_merge; minor fixes
implemented TrieStats and filled for CompressedSparseTrie
implemented BidirectionalList::insert(iterator, BidirectionalList), BidirectionalList::clear() and
moved back to c++11 standard, c++17 actually not needed