Support for Franklin.jl julia code block.

[flyaflya]

The most popular static-site generator in Julia is Franklin.jl. You write markdown files and it translates those to into a website. Very cool!

The issue is that the code blocks for Franklin.jl start with ```julia:foo.

These code blocks do not get any highlighting. Might it be possible to support Franklin.jl code blocks so that the code is highlighted using Julia's highlighting syntax?

See here for more info on Franklin's syntax: https://franklinjl.org/code/#live_evaluation_julia

Thanks!