Use barrier to generate badges

[tfausak]

This fixes #102.

I decided to use barrier because it's what Stackage uses. Check out their badge handler to see how it works.

[tfausak]

Almost forgot to post screenshots! Before:

After:

[hdgarrood]

Looks great :)

Just one thing: I think I'd rather use the renderBadge function, since then I don't think we need to import the Internal module. Then I think you can use preEscapedToMarkup to turn the ByteString into Svg.

[tfausak]

👍 I had to use unsafeLazyByteString instead of preEscapedToMarkup because there's no ByteString instance for ToMarkup.

[hdgarrood]

Looks great, thanks!