C++1y binary literals and digit separator

Clang 3.4 supports both:
http://clang.llvm.org/cxx_status.html#cxx14

``` cpp
#include <iostream>

int main()
{
 int n = 1'000'000;
 std::cout << n << std::endl;

 unsigned char c = 0b0100'0000;
 std::cout << c << std::endl;

 return 0;
}
```

I'm new to Vim syntax files, but the following seems to work for binary literals:

``` vim
syn match cNumber display contained "0b[01]\+\(\'[01]\+\)*"
```
