minor adjustments #3
Description
My first version of URT was using std::make_unique only available in C++ 14, the last version is no longer using it but instead std::make_shared available in C++ 11, makefile for C++, setup.py for Cython and Makevars for Rcpp have been amended, C++ 14 is no longer required and URT can be compiled using C++ 11 only.