Use idiomatic C++ io.

[jrmuizel]

Note this changes the C++ compile time and run time.

[jrmuizel]

Before:

             CT (ms)  RT (ms)

clang debug     71       486
clang release   69       132

After:

             CT (ms)  RT (ms)

clang debug     310       491
clang release   330       133

[atilaneves]

If you add this as extra files instead of modifying the originals I'll merge it.