Provide a utility method on a url to determine if it matches any pattern
in a comma-separated list, similar to what one would find in `NO_PROXY`
environment variables.

Provide a method to determine if a given URL matches a host:port pattern
like the ones found in `NO_PROXY` environment variables.

Using a callback to set a resolve_url is not particularly idiomatic.
Deprecate it in favor of the `set_instance_url` and
`set_instance_pushurl` functions which can now be called from the
`git_remote_ready_cb` callback.

Introduce a new callback that fires when the remote is ready to connect.

Users may want to override the URL on a particular instance of a remote,
instead of updating the configuration.  Previously, users could use a
callback to do this, but this is not particularly idiomatic.

IPv6 addresses should be used identically internally; we should not
denote them with brackets in one operating system and without them in
another.

Disambiguate invalid specifications in `git_refspec__parse` so that
callers can determine the difference between invalid specifications and
actual errors.  No call sites wil propagagte this new error message to
an end-user, so there is no user-facing API change.