Askari::Schema::V0::Application (partially) validates an askari.yml.

Validation is complete except for:
  * annotations
  * types
  * cell paths (version_column)

We also include the start of a type name validator.

Notice I call them type names.  Internally, types will be objects
satisfying some contract mostly concerned with converting primitives
to and from octet streams.

Type _names_ OTOH are small bits of arrays, hashes and primitives that
unambiguously _identify_ a single type.  They have no job except to
sit there and be pretty.  These are what we're handling now.

That said, the only true way to validate that an alleged name is legit
is to exhibit the corrosponding type.  Which means very soon we'll
need to exhibit something; stay tuned.