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/config/branch.go

@@ -0,0 +1,71 @@
+package config
+
+import (
+	"errors"
+
+	"gopkg.in/src-d/go-git.v4/plumbing"
+	format "gopkg.in/src-d/go-git.v4/plumbing/format/config"
+)
+
+var (
+	errBranchEmptyName    = errors.New("branch config: empty name")
+	errBranchInvalidMerge = errors.New("branch config: invalid merge")
+)
+
+// Branch contains information on the
+// local branches and which remote to track
+type Branch struct {
+	// Name of branch
+	Name string
+	// Remote name of remote to track
+	Remote string
+	// Merge is the local refspec for the branch
+	Merge plumbing.ReferenceName
+
+	raw *format.Subsection
+}
+
+// Validate validates fields of branch
+func (b *Branch) Validate() error {
+	if b.Name == "" {
+		return errBranchEmptyName
+	}
+
+	if b.Merge != "" && !b.Merge.IsBranch() {
+		return errBranchInvalidMerge
+	}
+
+	return nil
+}
+
+func (b *Branch) marshal() *format.Subsection {
+	if b.raw == nil {
+		b.raw = &format.Subsection{}
+	}
+
+	b.raw.Name = b.Name
+
+	if b.Remote == "" {
+		b.raw.RemoveOption(remoteSection)
+	} else {
+		b.raw.SetOption(remoteSection, b.Remote)
+	}
+
+	if b.Merge == "" {
+		b.raw.RemoveOption(mergeKey)
+	} else {
+		b.raw.SetOption(mergeKey, string(b.Merge))
+	}
+
+	return b.raw
+}
+
+func (b *Branch) unmarshal(s *format.Subsection) error {
+	b.raw = s
+
+	b.Name = b.raw.Name
+	b.Remote = b.raw.Options.Get(remoteSection)
+	b.Merge = plumbing.ReferenceName(b.raw.Options.Get(mergeKey))
+
+	return b.Validate()
+}