Nested Array (Jagged Array) support.

[jasonkuo41]

Background and Motivation

Currently, we do not plan on support nested array and jagged array at our initial release.
This is mainly because of the way of expressing "nested array" is "quite a lot" and is not enough to be covered by using Attributes.

Thus we will be relying on user code to express how a jagged array is represented.

Proposal A

Use of [Unwrap(string unwrapFunction)] to allow users to correctly unwrap the nested array types, this also allows them to read data and variables.

Proposal B

Use of [FormatNestedAs(Type unwrapType)] to allow users to use a schematic expression to express how they want certain fields to be. Also allowing users to accept the current class as constructor.

More proposal needed.