Organize menus better. No functional change.

Create an "Options" menu which, for now, only has the "Change difficulty" item.
Add separators to menu "Game".
Cosmetic changes.

Add missing punctuation.
Organize menus even better. No functional change.

As commented by waddlesplash. Thanks.
Merge pull request #3 from louisdem/master

Add a second menu for (available) options.