* added new threading functionality:
   * added support for clangs thread safety analysis + use it in some places (requires clang 3.5+, which is already required anyways ;))
   * added atomic_shared_ptr (partially based on std shared_ptr and N4162/N4260 proposals, with additional functionality)
   * added atomic_spin_lock (simple/straightforward lock based on atomic_flag)
   * added atomic_max (performs an atomic "object-val = max(object-val, desired-val)" operation)
   * added set_current_thread_name/get_current_thread_name to core (requires pthreads) and use it in thread_base and task
   * fixed race when setting the threads name in thread_base and task
   * when there is an exception in a task, also print the tasks thread name
 * added floor_inline_always macro to essentials (makes sure a function is (almost) always inlined)
 * added floor_hidden to essentials (marks a function as hidden / doesn't export it)
 * added logger::flush function (this will wait until the logger threads run method has run at least once)
 * added support to print the current time in each log msg (format: [%H:%M:%S.usecs]) and made it a config option (enabled by default)
 * added a config option to decide if colors should be used when printing the log type (enabled by default)
 * fixed logger::destroy() to only destroy the logger once
 * added %Y format option to the logger (does the same as %X, but fills the hex number with 0s up to its width)
 * updated README: require xcode 6.3+ (because 6.2 still uses an old clang ...), clarify how to disable cuda/opencl/openal and added llvm link