shortcuts to warning, info, danger and success

[merlos]

Added a few useful shortcuts

 ngToast.info('hello');
 // is the same as 
 ngToast.create({className: 'info', content:'hello' });

The pull request includes code, tests and doc

BTW, after working with ngToast I believe that Settings documentation (http://tamerayd.in/ngToast/#settings) should be included in the Readme just before Animations and the reference/link to this doc on the website. Thay way we would have all the docs in one single page.

Thanks. Juan.

[rictorres]

i like this 👍

[tameraydin]

Thanks! 1.5.2