Define a contract for `spec-tools/spec` and `schema-tools/schema`

[ikitommi]

Same contract for both for easy travel in between:

(schema-tools.core/spec
   integer?
   {:description "kikka"
    :type-hint :long
    :default 1})

(schema-tools.core/schema
   Long
   {:description "kikka"
    :default 1})

Relates https://github.com/metosin/spec-tools/issues/23