Uniqueify file names.

Mostly this just tweaks the names of some rpsec helpers.
Move Validation and Visitation out of V0 module.
Rename schema objects by adding `Schema` as a suffix.
Rename `tier` to `relation`.

This emphasizes how central the idea is about to become.  Since they,
not tables, are the largest typed construct, application authors will
spend most of their time working with them (and their components.)

Ideally this word would be "table", with the HBase notion of table
being relegated to a (critically important) implementation detail.
That would cause too much confusion though, so "relation" it is.