Experiment to fix the "sticky wicket" for @hartzell

Installers are often asked to install a core module.
To make that work, the index of the pinto repository
needs to include core modules so the installer can
decide if the local version is up to date.

So, we inject artifical records into the index for all
the core modules as-of the target_perl_version.  In
theory, an installer should never actually try to
install these modules because it should already have
them.  But that assumes that the target_perl_version
actually is the same version of perl that is running
the installer.

This seems really icky, but it just might work.
Fix tests.

Now that we stuff all the core modules in the index,
the size of a minimal 02packages file is much bigger.
The precise size still varies depending on the perl.
Just whitespace.
Make the fake records look like a real perl dist.

cpanm will skip installing a module if it looks like
it comes from a perl distribution.  So this should
help prevent an "accidental" attempt to install a perl
from a Pinto repository (because it doesn't really have
a perl, unless you explicitly pulled one).
Permit the root to be specified as an argument to the init command.

This helps people like @hartzell who are more accustomed to git.
But it breaks the interface -- now you must use the --stack option
to specify the name of the initial stack, instead of passing it
as an argument.  This probably makes sense, because you rarely
ever set the initial stack name, but you always have to specify
the root.  So you might as well make it easy to do so.
Document the --stack option of the init command.
Just POD formatting.
Update change log.