This termonology change affects lots of function names from `pkg/lib'
and `pkg/db' (former `pkg/pnr-db'), and it also affects some `raco
pkg' commands.
Existing package installations that are marked as 'pnr in a
local configuration are converted automatically to 'catalog, but any
existing "indexes" configuration must be changed to "catalogs".
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.
