Implement embedding / conversion model

[ivan-gammel]

As first PoC has shown viability of this approach, next step will be to implement the model for embedding entities and data type conversions.
The model must support reasonably deep embedding hierarchies and chaining of custom and built-in conversions, e.g.:

Embedding
Given following structure:

record A(@Embed B b) {}
record B(@Embed C c) {}
record C(@Embed D d) {}
record D(String value) {}

The following table could be mapped:

CREATE TABLE A (
  b_c_d_value VARCHAR(255)
);

Conversion
Given the following record:

record A(@Map(using = MyTimestampToInstant.class) MyTimestamp value) {}

The following table could be mapped, assuming conversion path from MyTimestamp to Instant and further to javax.sql.Timestamp.

CREATE TABLE A (
  value TIMESTAMP NOT NULL
);