mie: ctx is now used to query the type of a value

this allows value get_type callbacks to use mie_ctx to obtain mie_type pointers,
rather than having to define their own static versions of the type structs.

mie/const.c

@@ -10,7 +10,7 @@ void mie_const_init(struct mie_const *c, struct mie_type *type)
 	c->c_type = type;
 }
 
-static struct mie_type *get_type(struct mie_value *v)
+static struct mie_type *get_type(struct mie_value *v, struct mie_ctx *ctx)
 {
 	struct mie_const *c = MIE_CONST(v);
 	return c->c_type;