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.cpp

@@ -173,7 +173,7 @@ static void updatebuttonmappings(int bind)
     }
 }
 
-static void menuactionpress()
+static void menuactionpress(void)
 {
     switch (game.currentmenuname)
     {
@@ -1607,7 +1607,7 @@ static void menuactionpress()
     }
 }
 
-void titleinput()
+void titleinput(void)
 {
     //game.mx = (mouseX / 4);
     //game.my = (mouseY / 4);
@@ -1706,7 +1706,7 @@ void titleinput()
         script.startgamemode(game.mainmenu);
 }
 
-void gameinput()
+void gameinput(void)
 {
     //TODO mouse input
     //game.mx = (mouseX / 2);
@@ -2059,9 +2059,9 @@ void gameinput()
     }
 }
 
-static void mapmenuactionpress();
+static void mapmenuactionpress(void);
 
-void mapinput()
+void mapinput(void)
 {
     //TODO Mouse Input!
     //game.mx = (mouseX / 2);
@@ -2248,7 +2248,7 @@ void mapinput()
     }
 }
 
-static void mapmenuactionpress()
+static void mapmenuactionpress(void)
 {
     switch (game.menupage)
     {
@@ -2380,7 +2380,7 @@ static void mapmenuactionpress()
     }
 }
 
-void teleporterinput()
+void teleporterinput(void)
 {
     //Todo Mouseinput!
     //game.mx = (mouseX / 2);
@@ -2513,7 +2513,7 @@ void teleporterinput()
     }
 }
 
-void gamecompleteinput()
+void gamecompleteinput(void)
 {
     game.press_left = false;
     game.press_right = false;
@@ -2562,7 +2562,7 @@ void gamecompleteinput()
     }
 }
 
-void gamecompleteinput2()
+void gamecompleteinput2(void)
 {
     game.press_left = false;
     game.press_right = false;