Add possibility to define the background color of entities (black in ASCII, white in Unicode)

dungeonbattle/term_manager.py

@@ -13,6 +13,8 @@ class TermManager:  # pragma: no cover
         curses.cbreak()
         # make cursor invisible
         curses.curs_set(False)
+        # Enable colors
+        curses.start_color()
 
     def __enter__(self):
         return self