Explicitly declare void for all void parameter functions (#628)

Apparently in C, if you have `void test();`, it's completely okay to do
`test(2);`. The function will take in the argument, but just discard it
and throw it away. It's like a trash can, and a rude one at that. If you
declare it like `void test(void);`, this is prevented.

This is not a problem in C++ - doing `void test();` and `test(2);` is
guaranteed to result in a compile error (this also means that right now,
at least in all `.cpp` files, nobody is ever calling a void parameter
function with arguments and having their arguments be thrown away).
However, we may not be using C++ in the future, so I just want to lay
down the precedent that if a function takes in no arguments, you must
explicitly declare it as such.

I would've added `-Wstrict-prototypes`, but it produces an annoying
warning message saying it doesn't work in C++ mode if you're compiling
in C++ mode. So it can be added later.

desktop_version/src/Input.h

@@ -1,16 +1,16 @@
 #ifndef INPUT_H
 #define INPUT_H
 
-void titleinput();
+void titleinput(void);
 
-void gameinput();
+void gameinput(void);
 
-void mapinput();
+void mapinput(void);
 
-void teleporterinput();
+void teleporterinput(void);
 
-void gamecompleteinput();
+void gamecompleteinput(void);
 
-void gamecompleteinput2();
+void gamecompleteinput2(void);
 
 #endif /* INPUT_H */