Added the authorsPie function code

lib/index.js

@@ -5,6 +5,7 @@ var Ul = require("ul")
   , CliBox = require("cli-box")
   , Couleurs = require("couleurs")()
   , Gry = require("gry")
+  , IsThere = require("is-there")
   ;
 
 // Constants
@@ -401,5 +402,19 @@ GitStats.ansiCalendar = function (data, callback) {
 };
 
 GitStats.authorsPie = function (options, callback) {
+    if (typeof options === "string") {
+        options = {
+            repo: options
+        };
+    }
 
+    if (!IsThere.sync(options.repo)) {
+        return callback(new Error("Repository is missing."));
+    }
+
+    var repo = new Gry(options.repo);
+    repo.exec("shortlog -s -n --all", function (err, stdout) {
+        if (err) { return callback(err); }
+        console.log(stdout);
+    });
 };