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?

tests/cases/test_print.c

@@ -10,7 +10,7 @@ void count(const char* msg) {
 	counter++;
 }
 
-int test_callbacks() {
+int test_callbacks(void) {
 	//set a custom print callback, invoke it, and reset
 	{
 		//setup
@@ -95,7 +95,7 @@ int test_callbacks() {
 	return 0;
 }
 
-int main() {
+int main(void) {
 	//run each test set, returning the total errors given
 	int total = 0, res = 0;