If the argument table generator isn't able to reach a file that is
supposed to read, the two most likely causes are:
- The source .md documentation file that is requesting the table has a
typo in the path.
- The file with the arguments isn't there, for some reason.
In either case, we don't want the server to fail silently-ish and
display the docs as if there was no arguments for that endpoint. That's
why the most logic thing to do is to raise an exception and let the
admins know that there's something wrong.
This commit does the following:
* Move the Arguments table data from stream-message.md and
private-message.md to a JSON file.
* Add a Markdown extension that allows one to include and render
a table from a JSON file like so:
{generate_arguments_table|arguments.json|private-stream.md}
* Use Bootstrap's .table class to format the table instead of
relying on custom CSS.
