Display new window size (in pixels) in options

When changing the window x/y size in options, the new size (in pixels)
of the window will be displayed, so no more trial and error guessing to
get the window close to your preferred size.

As part of this commit, two new functions, ```projected_window_width(int column_count)``` and ```projected_window_height(int row_count)``` have been added to ```catacurse.h```, so they are usable for future enhancements if needed.

![image](https://f.cloud.github.com/assets/6007524/1640845/aedf3278-5843-11e3-8227-dddbafbfd663.png)