Fixed compilation and linkage on Win with MSVS2013 and WinSDK8.1
Add WIN81_SDK_DIR config variable
Use PrismaticMath::round() instead of round().
Minor changes in UpdatesProcessor.{h,c}pp
Rewrite logging code in main.cpp.

Created LogWriter class with all log-specific code.
Removed unnessesary stream.flush() calls and minimized
  time under locked mutex.
Expected no behavior change.
Change information about OS X build prerequisites
Use std::cerr instead of std::cout for any log message.
Move grabbers configuration from defs.h to configure-grabbers.prf project file.
Merge pull request #2 from dreamer-dead/logwriter

Rewrite logging code in main.cpp.
Merge pull request #1 from dreamer-dead/msvs2013_win81

MSVS2013&WinSDK8.1
Merge pull request #7 from dreamer-dead/configure-grabbers

Move grabbers configuration from defs.h to configure-grabbers.prf
Fix compilation with Mac SDK below 10.9 and clear some warnings.
Add QMAKE_MAC_SDK_OVERRIDE config variable.