The complexity of the arg parsing is increasing somewhat because we're
adding more features to cheddar, so to set us up for that this
switches the arg parsing to the somewhat more flexible clap.
Change-Id: I187bc0c1b6c6bd596fa0f6bb494b04e335262ba9
Reviewed-on: https://cl.tvl.fyi/c/depot/+/445
Reviewed-by: lukegb <lukegb@tvl.fyi>
Reviewed-by: tazjin <mail@tazj.in>
Generalises the two bits of the program that will be required either
way (extension parsing and syntax loading).
A dependency on Comrak is introduced as I think GitHub-flavoured
Markdown (with all its fancy extensions) is desirable!
The first step with this tool will be to use it as a source-filter for
cgit. The second step is to use it as the Markdown renderer by
depending on one of the Markdown libraries, with integration for
rendering code snippets directly.