add functions to redirect input/output

those two multiply the output into a file:

void redirect_output(const char *filename);
void redirect_output(std::string const &filename)

those two read everything from a file:

redirect_input(const char *filename);
redirect_input(std::string const& filename);

both can be resetted using:

void reset_input();
reset_output();

include/soi

@@ -77,7 +77,7 @@ soi_initializer soi_initializer_{false};
 } // end namespace soi
 
 #include "bits/soi-io.hpp"
-
+#include "bits/soi-redirect.hpp"
 #include "bits/soi-deprecate.hpp"
 
 #define int int64_t