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.
That is, limit the ending `raco setup' to the same collections
as the corresponding `raco pkg install' (droppping collections
that no longer exist afterward, of course).
Adds `pkg/pnr-db', `raco pkg index-copy', and `raco pkg index-show'.
Includes tools to build a database of modules that are supplied by
packages, which will be useful for a tool to recommend package
installs when a module is not found.
Also, document `pkg/lib' and add extra helper functions
for getting package information from a package name resolver.
