Askari::Application parses and (partially) validates an askari.yml.

Flush out the top-level keys, including many table, column family and
coprocessor defaults.  Next up are coprocessors, then tables.
Extract Validations, add a test suite.
Move Application under Askari::Schema.
Here's schema validation for coprocessors, as well as common attrs.

The common ones being label, description and metadata, which will also
appear on tables, tiers, column families, etc.
Applications expose and eagerly validate their coprocessors.
default_table_region_observers declares default observers for tables.
Here's table.

Applications do not yet construct tables, and tables do not yet have
tiers.
Application exposes and validates Tables.
Here's an unwired tier.

It knows nothing of paths (the syntax of the version_column key) or
types (its own yaml key.)
No need to validate twice, tables and coprocs do it on init.
A few more Application#table specs.
A few more Application#coprocessor specs.
Flush out Table#tiers.

There is still one unimplemented validation rule (uniqueness of column
family names across tiers.)
Add column families.

Tiers are aware of their column families, but families do not yet have
qualifiers.
Family names within a table must be unique, even across tiers.
Here are qualifiers.

Families are aware of their followers now.

Validation is complete except for:
  * annotations
  * types
  * cell paths (version_column)
Move everything under Schema::V0.
Start 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 to
exhibit the corrosponding type.  Which means very soon we'll need to
exhibit something; stay tuned.