Fixed run callback to preserve API compatibility

Callback parameters should be `(err, stdout, exitcode)`. The change introduced
by commit 587f600 was breaking API and also all unit-tests.

Updated README.md to show the callback parameters.

README.md

@@ -41,7 +41,7 @@ Lets take a look at some sample usage:
 
   nexpect.spawn("echo", ["hello"])
          .expect("hello")
-         .run(function (err) {
+         .run(function (err, stdout, exitcode) {
            if (!err) {
              console.log("hello was echoed");
            }
@@ -90,4 +90,4 @@ All tests are written with [vows][4]:
 [4]: http://vowsjs.org
 [5]: http://github.com/tmpvar
 [6]: http://github.com/marak
-[7]: http://github.com/indexzero
+[7]: http://github.com/indexzero

lib/nexpect.js

@@ -279,7 +279,7 @@ function chain (context) {
           return;
         }
 
-        callback(null, code, stdout);
+        callback(null, stdout, code);
       });
 
       return context.process;

test/nexpect-test.js

@@ -97,4 +97,4 @@ vows.describe('nexpect').addBatch({
       )
     }
   }
-}).export(module);
+}).export(module);