refactor(util/rb_tree): remove optimization that creates problems for
some compilers
refactor(util/memory_pool): simplify memory_pool, it is not a template anymore
refactor(*): remove dependency to thread_local C++11 keyword, the
current compilers have several bugs associated with it

We use the simpler __thread (gcc and clang) and
__declspec(thread) (visual studio).
refactor(*): remove dependency to thread_local C++11 keyword, the current compilers have several bugs associated with it