Merge errors and urls package into unified v2 package

To provide a single package with v2 API definitions, the locked down portions
of the API have been merged into a single package. References to exported items
will appear as v2.XXX, indicating their origin. The definitions in this package
will soon be locked down for change, acceppting only additions that will not
change protocol behavior.

api/v2/descriptors.go

@@ -1,4 +1,4 @@
-package errors
+package v2
 
 import "net/http"
 

api/v2/doc.go

@@ -0,0 +1,9 @@
+// Package v2 describes routes, urls and the error codes used in the Docker
+// Registry JSON HTTP API V2. In addition to declarations, descriptors are
+// provided for routes and error codes that can be used for implementation and
+// automatically generating documentation.
+//
+// Definitions here are considered to be locked down for the V2 registry api.
+// Any changes must be considered carefully and should not proceed without a
+// change proposal in docker core.
+package v2

api/v2/errors.go

@@ -1,12 +1,4 @@
-// Package errors describes the error codes that may be returned via the
-// Docker Registry JSON HTTP API V2. In addition to declaractions,
-// descriptions about the error codes and the conditions causing them are
-// avialable in detail.
-//
-// Error definitions here are considered to be locked down for the V2 registry
-// api. Any changes must be considered carefully and should not proceed
-// without a change proposal in docker core.
-package errors
+package v2
 
 import (
 	"fmt"

api/v2/errors_test.go

@@ -1,4 +1,4 @@
-package errors
+package v2
 
 import (
 	"encoding/json"

api/v2/routes.go

@@ -1,4 +1,4 @@
-package urls
+package v2
 
 import (
 	"github.com/docker/docker-registry/common"

api/v2/routes_test.go

@@ -1,4 +1,4 @@
-package urls
+package v2
 
 import (
 	"encoding/json"

api/v2/urls.go

@@ -1,4 +1,4 @@
-package urls
+package v2
 
 import (
 	"net/http"