Add Objecer interface

We do want to be able to accept generic objects in functions. Add this interface
so we can accept that instead of specific object types.

blob.go

@@ -20,6 +20,10 @@ type Blob struct {
 	cast_ptr *C.git_blob
 }
 
+func (b *Blob) AsObject() *Object {
+	return &b.Object
+}
+
 func (v *Blob) Size() int64 {
 	ret := int64(C.git_blob_rawsize(v.cast_ptr))
 	runtime.KeepAlive(v)

commit.go

@@ -18,6 +18,10 @@ type Commit struct {
 	cast_ptr *C.git_commit
 }
 
+func (c *Commit) AsObject() *Object {
+	return &c.Object
+}
+
 func (c *Commit) Message() string {
 	ret := C.GoString(C.git_commit_message(c.cast_ptr))
 	runtime.KeepAlive(c)

object.go

@@ -26,6 +26,11 @@ type Object struct {
 	repo *Repository
 }
 
+// Objecter lets us accept any kind of Git object in functions.
+type Objecter interface {
+	AsObject() *Object
+}
+
 func (t ObjectType) String() string {
 	switch t {
 	case ObjectAny:

tag.go

@@ -17,6 +17,10 @@ type Tag struct {
 	cast_ptr *C.git_tag
 }
 
+func (t *Tag) AsObject() *Object {
+	return &t.Object
+}
+
 func (t Tag) Message() string {
 	ret := C.GoString(C.git_tag_message(t.cast_ptr))
 	runtime.KeepAlive(t)

tree.go

@@ -27,6 +27,10 @@ type Tree struct {
 	cast_ptr *C.git_tree
 }
 
+func (t *Tree) AsObject() *Object {
+	return &t.Object
+}
+
 type TreeEntry struct {
 	Name     string
 	Id       *Oid