Perform a callback on each reference in the repository.
Using the list_flags parameter, the references may be filtered by
type (GIT_REF_OID or GIT_REF_SYMBOLIC) or using a bitwise OR of
git_ref_t values. To include packed refs, include GIT_REF_PACKED.
For convenience, use the value GIT_REF_LISTALL to obtain all
references, including packed ones.
The callback function will be called for each reference in the
repository, receiving the name of the reference and the payload value
passed to this method. Returning a non-zero value from the callback
will terminate the iteration.
Filtering flags for the reference listing.
Additional data to pass to the callback
0 on success, GIT_EUSER on non-zero callback, or error code