e5a260ad25
A ref goes into the archive URL verbatim and an explicit url goes to curl
as a positional, so both could name one thing and fetch another.
- reject "#", "?", "%", "[", "]", "{" and "}" in a tag or branch, which
curl or the server would turn into a different path
- pass "--" before the url so curl cannot read it as an option
- document the ref rules in README and the help file