Organise workspace crates and consolidate Cargo.toml manifest properties/dependencies

[Swoorup]

Simplify hacking on this repo by

• Allowing to change the version from a single Cargo.toml instead of multiple crates.
• Single place to update external dependency version instead of multiple cargo.toml's

[Maxxen]

This is def. a good idea, I'll pick this up and solve the conflicts after next release

[Swoorup]

Sure, I based few more changes, that fixes quite a far bit of the issues with appender (including adding support of union types and works well with nested types) atop this branch. Would be great to have it in. Let me know if anything is needed.

😃