move plumbing from top level package to plumbing (#183)

* plumbing: rename Object -> EncodedObject.

* plumbing/storer: rename ObjectStorer -> EncodedObjectStorer.

* move difftree to plumbing/difftree.

* move diff -> utils/diff

* make Object/Tag/Blob/Tree/Commit/File depend on storer.

* Object and its implementations now depend only on
  storer.EncodedObjectStorer, not git.Repository.
* Tests are decoupled accordingly.

* move Object/Commit/File/Tag/Tree to plumbing/object.

* move Object/Commit/File/Tag/Tree to plumbing/object.
* move checkClose to utils/ioutil.

* move RevListObjects to plumbing/revlist.Objects.

* move DiffTree to plumbing/difftree package.

* rename files with plural nouns to singular

* plumbing/object: add GetBlob/GetCommit/GetTag/GetTree.

1 files changed, 1 insertions, 25 deletions

diff --git a/common.go b/common.go
index aee932f..9c642ed 100644
--- a/common.go
+++ b/common.go
@@ -1,7 +1,6 @@
 package git
 
 import (
-	"io"
 	"strings"
 
 	"gopkg.in/src-d/go-git.v4/config"
@@ -13,7 +12,7 @@ import (
 // information in an system directory (such as `.git`) and others
 // implementations are in memmory being ephemeral
 type Storer interface {
-	storer.ObjectStorer
+	storer.EncodedObjectStorer
 	storer.ReferenceStorer
 	config.ConfigStorer
 }
@@ -34,26 +33,3 @@ func countLines(s string) int {
 
 	return nEOL + 1
 }
-
-// checkClose is used with defer to close the given io.Closer and check its
-// returned error value. If Close returns an error and the given *error
-// is not nil, *error is set to the error returned by Close.
-//
-// checkClose is typically used with named return values like so:
-//
-//   func do(obj *Object) (err error) {
-//     w, err := obj.Writer()
-//     if err != nil {
-//       return nil
-//     }
-//     defer checkClose(w, &err)
-//     // work with w
-//   }
-func checkClose(c io.Closer, err *error) {
-	if cerr := c.Close(); cerr != nil && *err == nil {
-		*err = cerr
-	}
-}
-
-// DateFormat is the format being use in the orignal git implementation
-const DateFormat = "Mon Jan 02 15:04:05 2006 -0700"