Added cache support

* Updated dependencies and package info (and remove `vow` and `vow-fs` dependencies)
* Removed unnecessary method `_getOptions()`
* Added cache (using `needRebuild` and `saveCache` methods)
* Remove node.js 0.8 from test cause of
```
npm ERR! Error: No compatible version found: date-now@'^0.1.4'
npm ERR! Valid install targets:
npm ERR! ["0.1.0","0.1.1","0.1.3","0.1.2","0.1.4","1.0.0"]
npm ERR!     at installTargetsError (/home/travis/.nvm/v0.8.26/lib/node_modules/npm/lib/cache.js:719:10)
npm ERR!     at /home/travis/.nvm/v0.8.26/lib/node_modules/npm/lib/cache.js:641:10
npm ERR!     at saved (/home/travis/.nvm/v0.8.26/lib/node_modules/npm/node_modules/npm-registry-client/lib/get.js:138:7)
npm ERR!     at Object.oncomplete (fs.js:297:15)
npm ERR! If you need help, you may report this log at:
npm ERR!     <http://github.com/isaacs/npm/issues>
npm ERR! or email it to:
npm ERR!     <npm-@googlegroups.com>
npm ERR! System Linux 2.6.32-042stab079.5
npm ERR! command "/home/travis/.nvm/v0.8.26/bin/node" "/home/travis/.nvm/v0.8.26/bin/npm" "install"
npm ERR! cwd /home/travis/build/enb-make/enb-autoprefixer
npm ERR! node -v v0.8.26
```

Don’t forget exec `npm version 0.1.1` and push commit and tags to github and publish the npm package after merging!