Explore mechanisms for defining external binary representations

[jverkoey]

Swift Codable is able to generate encoding and decoding implementations for free because of the availability of key/value containers. Binary Codable does not support key/value containers, so it is not presently possible to map properties to external representations without making some potentially scary assumptions about order.

A completely generalized solution to this problem is not desired due to the need for conditional encoding/decoding paths in complex cases. Solving conditional coding is considered a non-goal for this task; in such cases custom implementations of encoding/decoding are encouraged instead.

A successful solution to this task will meet the following requirements:

• It is possible to map properties to regions of memory bi-directionally (encoding + decoding).
• It is possible to map BinaryCodable entities to regions of memory bi-directionally (encoding + decoding).
• Such a definition only needs to be made once for a given object, similar to the CodingKeys pattern in Swift Codable.