Added ghRepo.getBlob(String) method

Signed-off-by: Kanstantsin Shautsou <kanstantsin.sha@gmail.com>

src/main/java/org/kohsuke/github/GHBlob.java

@@ -0,0 +1,30 @@
+package org.kohsuke.github;
+
+/**
+ * @author Kanstantsin Shautsou
+ * @see <a href="https://developer.github.com/v3/git/blobs/#get-a-blob">Get a blob</a>
+ */
+public class GHBlob {
+    private String content, encoding, url, sha;
+    private long size;
+
+    public String getEncoding() {
+        return encoding;
+    }
+
+    public String getUrl() {
+        return url;
+    }
+
+    public String getSha() {
+        return sha;
+    }
+
+    public long getSize() {
+        return size;
+    }
+
+    public String getContent() {
+        return content;
+    }
+}

src/main/java/org/kohsuke/github/GHRepository.java

@@ -817,6 +817,14 @@ public class GHRepository extends GHObject {
         return root.retrieve().to(url, GHTree.class).wrap(root);
     }
 
+    /**
+     * @see <a href="https://developer.github.com/v3/git/blobs/#get-a-blob">Get a blob</a>
+     */
+    public GHBlob getBlob(String blobSha) throws IOException {
+        String target = getApiTailUrl("git/blobs/" + blobSha);
+        return root.retrieve().to(target, GHBlob.class);
+    }
+
     /**
      * Gets a commit object in this repository.
      */

src/main/java/org/kohsuke/github/GHTreeEntry.java

@@ -54,14 +54,14 @@ public class GHTreeEntry {
 
 
     /**
-     * SHA1 of this object.
+     * SHA1 of this blob object.
      */
     public String getSha() {
         return sha;
     }
 
     /**
-     * API URL to this Git data, such as
+     * API URL to this Git blob data, such as
      * https://api.github.com/repos/jenkinsci
      * /jenkins/git/commits/b72322675eb0114363a9a86e9ad5a170d1d07ac0
      */