Added simple assignment, read more

I was coding earlier this week, but my brain was so foggy I ended up not
knowing what I was doing. After a few days break, I've cleaned up the
mess, which took hours.

Changes:
* Variables can be assigned
* Added new value types as placeholders
* Added 'compare' and 'assign' to the AST
* Added duplicate opcode
* Added functions to copy and free values
* Max name length is 255 chars
* Compound assigns are squeezed into one word

To be completed:

* Tests for this commit's changes
* Compound assignments
* Variable access

source/toy_stack.h

@@ -6,7 +6,7 @@
 typedef struct Toy_Stack { //32 | 64 BITNESS
 	unsigned int capacity; //4  | 4
 	unsigned int count;    //4  | 4
-	char data[];           //-  | -
+	Toy_Value data[];      //-  | -
 } Toy_Stack;               //8  | 8
 
 TOY_API Toy_Stack* Toy_allocateStack();