Fix warning messages during compilation

[xirius]

Hi, I have few warning messages during compilation (clang++). It would be nice to fix them.

---

NanoLog/NanoLog.cpp:57:34: warning: format specifies type 'unsigned long long' but the argument has type 'unsigned long' [-Wformat]
sprintf(microseconds, "%06llu", timestamp % 1000000);
                       ~~~~~~   ^~~~~~~~~~~~~~~~~~~
                       %06lu
NanoLog/NanoLog.cpp:349:11: warning: braces around scalar initializer [-Wbraced-scalar-init]
: flag{ATOMIC_FLAG_INIT}
       ^~~~~~~~~~~~~~~~
.../include/c++/6.3.0/bits/atomic_base.h:157:26: note: expanded from macro 'ATOMIC_FLAG_INIT'
#define ATOMIC_FLAG_INIT { 0 }
                         ^~~~~
NanoLog/NanoLog.cpp:484:15: warning: braces around scalar initializer [-Wbraced-scalar-init]
, m_flag{ATOMIC_FLAG_INIT}
         ^~~~~~~~~~~~~~~~
.../include/c++/6.3.0/bits/atomic_base.h:157:26: note: expanded from macro 'ATOMIC_FLAG_INIT'
#define ATOMIC_FLAG_INIT { 0 }
                         ^~~~~