mrkd started enforcing the `name -- short description` style of top-level
headings somewhere, and was thus failing to build the man-pages. I swapped
the title and with the existing short description to make it work
again. `mrkd` will automatically infer the section from the filename so no
need to put it in the title as well.
In addition I removed the "last updated" lines at the bottom since they are
out of date at best, and misleading at the worst. If we want to keep them, I'd
suggest generating them from the commit that last touched them.
delinvoice was orginally documented to only allow deletion of unpaid
invoices, but there might be reasons to delete paid ones or unexpired ones.
But we have to avoid the race where someone pays as it's deleted: the
easiest way is to have the caller tell us the status, and fail if
it's wrong.
Fixes: #477
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>