All kinds of things

- Add modified BSD license
- Initial test runner github action
- Add is_{type} functions
- export kiwi.Error metatable such that it appears like a class.
- Allow Expression.new to take nil for terms
- Initial set of specs

ckiwi/ckiwi.h

@@ -56,7 +56,7 @@ const char* kiwi_var_name(KiwiVarRef var);
 void kiwi_var_set_name(KiwiVarRef var, const char* name);
 double kiwi_var_value(KiwiVarRef var);
 void kiwi_var_set_value(KiwiVarRef var, double value);
-int kiwi_var_eq(KiwiVarRef var, KiwiVarRef other);
+bool kiwi_var_eq(KiwiVarRef var, KiwiVarRef other);
 
 void kiwi_expression_del_vars(KiwiExpression* expr);