chore(Grunt): switch from Rake to Grunt

Migrates the Angular project from Rake to Grunt.

Benefits:
- Drops Ruby dependency
- Lowers barrier to entry for contributions from JavaScript ninjas
- Simplifies the Angular project setup and build process
- Adopts industry-standard tools specific to JavaScript projects
- Support building angular.js on Windows platform (really?!? why?!?)

BREAKING CHANGE: Rake is completely replaced by Grunt. Below are the deprecated Rake tasks and their Grunt equivalents:

rake --> grunt
rake package --> grunt package
rake init --> N/A
rake clean --> grunt clean
rake concat_scenario --> grunt build:scenario
rake concat --> grunt build
rake concat_scenario --> grunt build:scenario
rake minify --> grunt minify
rake version --> grunt write:version
rake docs --> grunt docs
rake webserver --> grunt webserver
rake test --> grunt test
rake test:unit --> grunt test:unit
rake test:<jqlite|jquery|modules|e2e> --> grunt test:<jqlite|jquery|modules|end2end|e2e>
rake test[Firefox+Safari] --> grunt test --browsers Firefox,Safari
rake test[Safari] --> grunt test --browsers Safari
rake autotest --> grunt autotest

NOTES:
* For convenience grunt test:e2e starts a webserver for you, while grunt test:end2end doesn't.
  Use grunt test:end2end if you already have the webserver running.
* Removes duplicate entry for Describe.js in the angularScenario section of angularFiles.js
* Updates docs/src/gen-docs.js to use #done intead of the deprecated #end
* Uses grunt-contrib-connect instead of lib/nodeserver (removed)
* Removes nodeserver.sh, travis now uses grunt webserver
* Built and minified files are identical to Rake's output, with the exception of one less
  character for git revisions (using --short) and a couple minor whitespace differences

Closes #199

README.md

@@ -21,21 +21,19 @@ Building AngularJS
 ---------
 [Once you have your environment setup](http://docs.angularjs.org/misc/contribute) just run:
 
-    rake package
+    grunt package
 
 
 Running Tests
 -------------
 To execute all unit tests, use:
 
-    rake test:unit
+    grunt test:unit
 
 To execute end-to-end (e2e) tests, use:
 
-    rake package
-    rake webserver &
-    rake test:e2e
+    grunt package
+    grunt test:e2e
 
-To learn more about the rake tasks, run `rake -T` and also read our
-[contribution guidelines](http://docs.angularjs.org/misc/contribute) and instructions in this
-[commit message](https://github.com/angular/angular.js/commit/9d168f058f9c6d7eeae0daa7cb72ea4e02a0003a).
+To learn more about the grunt tasks, run `grunt --help` and also read our
+[contribution guidelines](http://docs.angularjs.org/misc/contribute).