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/Render.cpp

@@ -27,7 +27,7 @@ static int inline FLIP(int ypos)
     return ypos;
 }
 
-static inline void drawslowdowntext()
+static inline void drawslowdowntext(void)
 {
     switch (game.slowdown)
     {
@@ -46,7 +46,7 @@ static inline void drawslowdowntext()
     }
 }
 
-static void menurender()
+static void menurender(void)
 {
     int temp = 50;
 
@@ -1218,7 +1218,7 @@ void titlerender()
     graphics.renderwithscreeneffects();
 }
 
-void gamecompleterender()
+void gamecompleterender(void)
 {
     FillRect(graphics.backBuffer, 0x000000);
 
@@ -1364,7 +1364,7 @@ void gamecompleterender()
     graphics.render();
 }
 
-void gamecompleterender2()
+void gamecompleterender2(void)
 {
     FillRect(graphics.backBuffer, 0x000000);
 
@@ -1396,7 +1396,7 @@ void gamecompleterender2()
     graphics.render();
 }
 
-void gamerender()
+void gamerender(void)
 {
 
 
@@ -1710,7 +1710,7 @@ void gamerender()
     graphics.renderwithscreeneffects();
 }
 
-void maprender()
+void maprender(void)
 {
     FillRect(graphics.backBuffer, 0x000000);
 
@@ -2467,7 +2467,7 @@ void maprender()
     }
 }
 
-void teleporterrender()
+void teleporterrender(void)
 {
     FillRect(graphics.backBuffer, 0x000000);
     int tempx;