Remove ==, not==, and order[<,<=,>,>=].

This unifies equality and comparison checking. Before, we had
separate functions and vm opcodes for comparing general values vs.
for comparing numbers, where the numberic functions were polymorphic and
had special cases for handling NaNs. By unfiying them, abstract types
can now better integrate with other number types and behave as keys.

For now, the old functions are aliased but will eventually be removed.

src/core/thread.c

@@ -393,6 +393,8 @@ static JanetAbstractType Thread_AT = {
     NULL,
     NULL,
     NULL,
+    NULL,
+    NULL,
     NULL
 };