remove debugging `log-error'
raco setup: protect against bad info-domain cache
raco setup: --tidy mode (as needed by `raco pkg remove') and more

When a collection disappears, then documentation and metadata
cross-references need fixing up based on everything that remains
available, even though other setup actions are confined to
collections that are specifically relevant to the packages. The
new `--tidy' mode takes care of that.

Package installation now also provides `--avoid-main' when working
with packages in a scope other than installation scope, and `raco
setup' now better respects `--avoid-main' to avoid creating
executables or re-running documentation.

Also, revise the `raco' documentation to better orient it toward the
package manager.
demote some `raco' commands

The commands `link', `pack', and `unpack' are now
discouraged in favor of `pkg'.