Add README badges

I figured adding the following badges to grunt-contrib projects would be useful: (example using grunt-contrib-stylus)

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# grunt-contrib-stylus v0.13.2
[![NPM version](https://badge.fury.io/js/grunt-contrib-stylus.svg)](http://badge.fury.io/js/grunt-contrib-stylus) [![Build Status](https://travis-ci.org/gruntjs/grunt-contrib-stylus.svg?branch=master)](https://travis-ci.org/gruntjs/grunt-contrib-stylus) [![Dependency Status](https://david-dm.org/gruntjs/grunt-contrib-stylus.svg)](https://david-dm.org/gruntjs/grunt-contrib-stylus) [![devDependency Status](https://david-dm.org/gruntjs/grunt-contrib-stylus/dev-status.svg)](https://david-dm.org/gruntjs/grunt-contrib-stylus#info=devDependencies) [![Built with Grunt](https://cdn.gruntjs.com/builtwith.png)](http://gruntjs.com/)

> Compile Stylus files to CSS.

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If theres any that you think do not belong, let me know and I'll take it out. Also, I can go through all the contrib projects to update the READMEs, and try to update any out of date dependencies so you can get them all up to date.

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**Changes:**
- Added npm version badge
- Updated travis badge to use svg version
- Added David DM badges
- Added Built with Grunt badge

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If you need anything else in this PR, please let me know. Thanks