Pattern for more detailed types

[rufuspollock]

Many platforms/tools including SQL have a more detailed set of types (e.g. long integer) than Table Schema. This may be relevant for serialization and deserialization reliably. We have intentionally not included lots of types into Table Schema as it quickly gets complex (and you still don't support everyone).

What is proposed here is some standard pattern for adding additional information on types to Table Schema, esp a model of subtypes e.g. that something is a long integer cf #277 .

Tasks

• Review existing important tools and their type lists e.g. SQL, Spark, BigQuery, ...
• Develop the pattern