Implement git refs API for listing references (branches, tags and other) (#5354)

* Inital routes to git refs api

* Git refs API implementation

* Update swagger

* Fix copyright

* Make swagger happy add basic test

* Fix test

* Fix test again :)

vendor/gopkg.in/src-d/go-git.v4/plumbing/object/difftree.go

@@ -0,0 +1,37 @@
+package object
+
+import (
+	"bytes"
+	"context"
+
+	"gopkg.in/src-d/go-git.v4/utils/merkletrie"
+	"gopkg.in/src-d/go-git.v4/utils/merkletrie/noder"
+)
+
+// DiffTree compares the content and mode of the blobs found via two
+// tree objects.
+func DiffTree(a, b *Tree) (Changes, error) {
+	return DiffTreeContext(context.Background(), a, b)
+}
+
+// DiffTree compares the content and mode of the blobs found via two
+// tree objects. Provided context must be non-nil.
+// An error will be return if context expires
+func DiffTreeContext(ctx context.Context, a, b *Tree) (Changes, error) {
+	from := NewTreeRootNode(a)
+	to := NewTreeRootNode(b)
+
+	hashEqual := func(a, b noder.Hasher) bool {
+		return bytes.Equal(a.Hash(), b.Hash())
+	}
+
+	merkletrieChanges, err := merkletrie.DiffTreeContext(ctx, from, to, hashEqual)
+	if err != nil {
+		if err == merkletrie.ErrCanceled {
+			return nil, ErrCanceled
+		}
+		return nil, err
+	}
+
+	return newChanges(merkletrieChanges)
+}