Fixes another off-by-one issue when diffing with caching

Refactored commands and blame annotations

src/commands/showBlame.ts

@@ -0,0 +1,27 @@
+'use strict'
+import {TextEditor, TextEditorEdit, Uri} from 'vscode';
+import BlameAnnotationController from '../blameAnnotationController';
+import {EditorCommand} from './commands';
+import {Commands} from '../constants';
+import GitProvider from '../gitProvider';
+
+export default class ShowBlameCommand extends EditorCommand {
+    constructor(private git: GitProvider, private annotationController: BlameAnnotationController) {
+        super(Commands.ShowBlame);
+    }
+
+    execute(editor: TextEditor, edit: TextEditorEdit, uri?: Uri, sha?: string) {
+        if (sha) {
+            return this.annotationController.toggleBlameAnnotation(editor, sha);
+        }
+
+        if (!(uri instanceof Uri)) {
+            if (!editor.document) return;
+            uri = editor.document.uri;
+        }
+
+        return this.git.getBlameForLine(uri.fsPath, editor.selection.active.line)
+            .catch(ex => console.error('[GitLens.ShowBlameCommand]', `getBlameForLine(${editor.selection.active.line})`, ex))
+            .then(blame => this.annotationController.showBlameAnnotation(editor, blame && blame.commit.sha));
+    }
+}