lua/Lua: Support Lua 5.2.
Makefile: Update to C++11.
gui: Update to SFML 2.1.
Use C++11 smart pointers.
Use C++11 chrono clock.
Use C++11 threads and mutexes.
Use C++11 std::function.
Use C++11 unordered_map and unordered_set.
Use C++11 range-based loop.
Use C++11 std::bind.
Makefile: Remove unused Boost libraries.
Remove copyright notices from individual files.

We already have LICENSE and AUTHORS, and Git knows who did what.