feat: Add struct git_reference_iterator

Added struct `git_reference_iterator`.
See git2/sys/refdb_backend.h line 35.

Author: tecc

libgit2-sys/lib.rs

@@ -112,7 +112,7 @@ pub const GIT_CONFIG_BACKEND_VERSION: c_uint = 1;
 pub struct git_config_backend_memory_options {
     pub version: c_uint,
     pub backend_type: *const c_char,
-    pub origin_path: *const c_char
+    pub origin_path: *const c_char,
 }
 
 pub const GIT_CONFIG_BACKEND_MEMORY_OPTIONS_VERSION: c_uint = 1;
@@ -121,7 +121,15 @@ pub enum git_index {}
 pub enum git_index_conflict_iterator {}
 pub enum git_object {}
 pub enum git_reference {}
-pub enum git_reference_iterator {}
+
+#[repr(C)]
+pub struct git_reference_iterator {
+    pub db: *mut git_refdb,
+    pub next: Option<fn(*mut *mut git_reference, *mut git_reference_iterator) -> c_int>,
+    pub next_name: Option<fn(*mut *const c_char, *mut git_reference_iterator) -> c_int>,
+    pub free: Option<fn(*mut git_reference_iterator)>,
+}
+
 pub enum git_annotated_commit {}
 pub enum git_refdb {}
 pub enum git_refspec {}