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/Ent.h

@@ -8,10 +8,10 @@
 class entclass
 {
 public:
-    entclass();
-    void clear();
+    entclass(void);
+    void clear(void);
 
-    bool outside();
+    bool outside(void);
 
     void setenemy(int t);
 
@@ -19,9 +19,9 @@ public:
 
     void settreadmillcolour(int rx, int ry);
 
-    void updatecolour();
+    void updatecolour(void);
 
-    bool ishumanoid();
+    bool ishumanoid(void);
 
 public:
     //Fundamentals