message: Remove `using namespace` clauses from MapViewStateIO.cpp
diff: #include <stdexcept>
  #include <iostream>
  -using namespace NAS2D;
  -using namespace NAS2D::Xml;
  -
  /// \fixme Fugly, find a sane way to do this.
  extern const std::string MAP_TERRAIN_EXTENSION = "_a.png";
  