buildsys: allow re-building synopsis & opts files standalone

buildsys: allow re-building synopsis & opts files standalone

Add two new make targets 'update-static', 'clean-static' which split
out functionality from the 'update' target.
As the latter uses the long duration `make all` anybody which just
wants to see the current synopsis (e.g., when improving a chapter)
spends a lot time waiting here.

The new target clean or update (generate) specifically just the
synopsis, opts, apidata and firewall macro files from the current
installed package versions, allowing faster build times when one does
frequent edit-build cycles.