Refactored error handling

Now uses base error class which has an abstract function for overiding how it is displayed to the console.

Parser/src/AST-LLVM.cpp

@@ -1,5 +1,7 @@
 #include <Parser.h>
 
+#include <ThrowIf.h>
+
 #include <LLVM.h>
 #include <Util.h>
 #include <AST.h>