epkg/verifyall: Correct behavior

equery requires that we specify a glob pattern for the packages to
verify, so let's give it '*' so it does what we want.
epkg/autoremove: New command

Does the standard emerge --depclean usually done after an upgrade pass
epkg/verify*: Only show files which failed to pass

This passes -o to equery clean to limit output to only those files which
failed to pass the checks.
epkg: Allow more passing of arbitrary parameters

This adds passing of supplied parameters to the verifyall and sysinfo
commands
epkg: Add a much more thorough usage display

More thoroughly describes the usage of epkg and its subcommands.