markdown-include is GPL licensed.
Also, rewrite it as a block processor, so that it works correctly
inside indented blocks.
Signed-off-by: Anders Kaseorg <anders@zulip.com>
We let Markdown increment the list step numbers, which is more
reliable than keeping track of numbered-steps manually.
Also, instead of linking to the CircleCI docs, we now have full
instructions for how to setup a webhook by modifying the circle.yml
file.