Pull markdown/syntax highlighting code out into their own tools

It would be nice to pull some things out into their own tools, likely outputting standalone documents. In particular:
  * markdown -> latex 
  * source code -> latex

however have a think on whether src_dirs Lumpy.toml key should be a glob of files allowing the inclusion of markdown files.

Such as: 
```toml
sources = ["src/**/*.md", "src/**/*.lean"]
```