Added CC_FORMAT_PRINTF(x,y) macro to warn on CCLog() format errors

Uses printf format. Enabled for GCC and clang.
Added CC_FORMAT_PRINTF to CCString

Added for CCString::initWithFormat() and CCString::createWithFormat().
Fixed warnings.
Merge pull request #2407 from sergey-shambir/attribute_format

Added __attribute__(__format__()) for CCLog and CCString