avro_generic_value_free is not exposed via avro/generic.h

The C bindings documentation refers to the avro_generic_value_free function.

#include <avro.h>

avro_value_iface_t *avro_generic_class_from_schema(avro_schema_t schema);
int avro_generic_value_new(const avro_value_iface_t *iface, avro_value_t *dest);
void avro_generic_value_free(avro_value_t *self);

But it doesn't seem to be exposed via avro/generic.h, so users can't see it by just including avro.h.
In addition, its signature in the document seems wrong. The right one is void avro_generic_value_free(const avro_value_iface_t *iface, void *self).