Allow pausing (Updated)

[merv1n34k]

This fixes #47 and closes #48.

What is added:

1. -r argument - if game save is exist and valid, the game resumes
2. G command - saves sudoku during the game
3. Game save file is stored in $XDG_STATE_HOME/nudoku/ if set, otherwise $HOME/.local/state/nudoku/ is used.
4. After game resumes the game save file is deleted
5. Game save file name is defined as state.save

[merv1n34k]

Thanks for the review!

[merv1n34k]

Improvements:

1. Instead of program exit user will be notified he can't save/open file.
2. Updated get_saved_file_path to handle malloc properly, free fallback_path on exit.

[merv1n34k]

Also, think it would be better to update the documentation as well.

[jubalh]

See comment above

[jubalh]

Thanks!

[jubalh]

Let me know if you plan to work on more things.
I think to create a new release with your changes in the next days.

[merv1n34k]

Well, one more thing before the release is to update the potfiles :)
Would it be okay if I skip some translations?

[jubalh]

Would it be okay if I skip some translations?

Sure!