add Hex badges

Here are nice badges showing Hex version and downloads counter.

They are autogenerated by [shields.io](http://shields.io) service based on what's already been published to Hex.

If you'd like to peek how it looks like, see https://github.com/herenowcoder/reprise for example
Merge pull request #4 from herenowcoder/patch-1

Add Hex badges