Variable type annotation and SDK-level automatic serialization/deserialization

[camelop]

Migrated from: https://github.com/camelop/dds-dev/issues/15

Idea

For key-value pairs in the storage engine, allow optional type annotation so that SDK can learn the type of the variables to make smart serialization/deserialization decisions.

Potential implementation

For each key xxx::yyy:zz, add xxx:yyy:zz:__annotation which contains metadata about the original key.

For example, if 0xAA:some_computation:iamafloat64 is a float64 value, SDK can read 0xAA:some_computation:iamaflot64:__annotation which returns float64, then it can automatically and dynamically do deserialization when loading the value. This might be helpful for some languages.

Discussion

As a strengthened version, one can also augment this mechanism to implement schema checking for strict data format.