Use full namespace prefix instead of "using" statement

[UVCAD]

There are many places use "using" statement to import namespace, it's easy to ruin the namespace. It's recommended to use full namespace prefix. The best practice is to use full namespace, remove all such code likes these:
using namespace Go;
using std::vector;
using std::swap;
using std::max;
using std::min;
using std::pair;
using std::make_pair;
using std::streamsize;
using std::endl;