Dug into pygments a bit while trying to figure out why the background color wasn't showing on my code blocks. I discovered the need to specify the CSS class in the get_style_defs call so it'll be added to the CSS selectors.

Without the arg to get_style_defs('.highlight'), this line wasn't present in the generated CSS (I assume because there would've been no selector for it):

.highlight { background: #242933; color: #d8dee9 }

Also, since I want to be able to specify a custom CSS class, I added an optional config entry for pygments.cssclass. This could also support those who may have existing styles selecting for the previously-used .hll selector.

Resolves #12