Cxx11

[lhmouse]

This commit adds reference implementations for C++11 threading facilities:

• once_flag
• mutex and timed_mutex
• recursive_mutex and recursive_timed_mutex
• condition_variable
• thread
• thread_specific_ptr (non-standard, inspired by boost)

This closes #77.

[lhmouse]

@frankhb We need some testcases at the moment.

[lhmouse]

Ready to merge?

[FrankHB]

LGTM.