Allow accessing puzzle and solution as array of integers

For GNOME Sudoku we will need some way to access the puzzle data. (Since we can't pass a C++ class into our C code, we want to somehow export it to a string or array.)  After messing around with changing all the print functions to accept an ostream as a parameter, planning to parse ints from a stringstream, I realized this would be a much easier approach.

Note that since I'm modifying qqwing.[ch]pp I unfortunately have to update the library's soname version, to avoid bug reports from distros that have packaged qqwing. (If only modifying main.cpp, this shouldn't be changed.)  This should really only be done once per release, but it's easy to forget.