Adds .gitignore checks to reduce blame calls

Caches failed blames to reduce blame calls
Only clear failed blames from cache on change/save
Add better error messages and handling

typings/ignore.d.ts

@@ -0,0 +1,10 @@
+declare module "ignore" {
+    namespace ignore {
+        interface Ignore {
+            add(patterns: string | Array<string> | Ignore): Ignore;
+            filter(paths: Array<string>): Array<string>;
+        }
+    }
+    function ignore(): ignore.Ignore;
+    export = ignore;
+}