ENHANCED: the toplevel interaction now supports RETURN as a synonym for "."

This is made possible due to the recent improvements by @notoria.

README.md

@@ -168,8 +168,8 @@ predicates it defines. For example, with the program shown above:
 ;  What = pure_world.
 ```
 
-Press `SPACE` to show further answers, if any exist. Press `.` to
-abort the search and return to the toplevel prompt.
+Press `SPACE` to show further answers, if any exist. Press `RETURN` or
+ `.` to abort the search and return to the toplevel prompt.
 Press `h` to show a help message.
 
 To quit Scryer Prolog, use the standard predicate `halt/0`:

src/prolog/toplevel.pl

@@ -162,7 +162,7 @@
     ;  C = h ->
        '$help_message',
        '$read_input'(ThreadedGoals, NewVarList)
-    ;  C = '.' ->
+    ;  member(C, ['\n', .]) ->
        nl, write(';  ...'), nl
     ; '$read_input'(ThreadedGoals, NewVarList)
     ).
@@ -170,7 +170,7 @@
 '$help_message' :-
     nl, nl,
     write('SPACE, "n" or ";": next solution, if any\n'),
-    write('".": stop enumeration\n'),
+    write('RETURN or ".": stop enumeration\n'),
     write('"h": display this help message\n'),
     write('"w": write terms without depth limit\n'),
     write('"p": print terms with depth limit\n\n').