Add an implementation of base types.

These will hold information about a type such as (possibly) the
interfaces it implements and the parameters it accepts.

src/basetype.c

@@ -0,0 +1,10 @@
+#include "basetype.h"
+#include "util.h"
+#include <stdlib.h>
+
+void libab_basetype_init(libab_basetype* basetype,
+        int n, const libab_basetype_param params[]) {
+    basetype->params = params;
+    basetype->count = n;
+}
+