implement toggle function

add some functions and simple UI to toggle(hide/show) dotfiles

fixes #1 

![2014-08-03 10 37 10](https://cloud.githubusercontent.com/assets/3864761/3790811/ec4bf394-1b1b-11e4-83f3-3ed6f542d551.png)

no, inline in the event statement https://github.com/sindresorhus/github-hide-files/pull/6/files#diff-a482ea1142029551c5e18434b60ea27aR37