Parser is reading variable declarations, read more

This is an incomplete process. It's supposed to be robust enough to
support the types of arrays and dictionaries, but arrays and
dictionaries aren't implemented in the literals yet, so that's my next
task.

I'll come back to variable declarations later.

source/scope.h

@@ -4,7 +4,7 @@
 #include "literal_dictionary.h"
 
 typedef struct Scope {
-	LiteralDictionary variables;
+	LiteralDictionary variables; //only allow identifiers as the keys
 	struct Scope* ancestor;
 	int references; //how many scopes point here
 } Scope;