Move executables to shoes-core

shoes is just an installation shell. We want a backend to be able to get
everything it needs--primary shoes, backend picker, etc. without
dependneing on that default installation.
README updates based on changes to shoes and shoes-core usage
No, really, don't commit shoes-backend
Fix for running from source on Windows
Windows seemed cranky about shoes --version when unqualified
Fix for overlapping text

When flowing text to a second layout, we would stop short of consuming
all the vertical space provided us, but then position the second layout
based on the height of the first layout. Sometimes this resulted in
overlapping text.

Instead, we will now keep putting text into into the first layout until
it completely fills the height--even if it goes over by a little--so
that we get a smoother flow into the second layout.