Reworked Toy_String as a union, enabled -Wpedantic

Toy now fits into the C spec.

Fixed #158

Addendum: MacOS test caught an error:

error: a function declaration without a prototype is deprecated in all versions of C

That took 3 attempts to fix correctly.

Addendum: 'No new line at the end of file' are you shitting me?

source/toy_stack.c

@@ -4,7 +4,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 
-Toy_Stack* Toy_allocateStack() {
+Toy_Stack* Toy_allocateStack(void) {
 	Toy_Stack* stack = malloc(TOY_STACK_INITIAL_CAPACITY * sizeof(Toy_Value) + sizeof(Toy_Stack));
 
 	if (stack == NULL) {