Support different styles of shields

[colinodell]

Shields.io offers shields in several different styles. It would be great if Shepherd could do the same. In particular, I'd really like to use the flat-square style for visual compatibility with my other shield images.

[kubawerlos]

@colinodell I have found a workaround to have a type coverage badge with a different style.

Each repo, except the badge has also coverage data.

So, all you have to do is use Shields.io with that data: https://img.shields.io/endpoint?label=type%20coverage&style=flat-square&url=https%3A%2F%2Fshepherd.dev%2Fviews%2Fcoverage_data.php%3Fcolinodell%2Findentation