upickle - usability and stability for 1.0

[szymon-rd]

Context

This issue is meant to track the progress in improving the toolkit libraries' usability and stability. This issue is created here to establish the toolkit's perspective in the discussion, especially the interoperability between the toolkit's libraries and usability with the definition used in the Toolkit.

Tasks

Below is the list of high-priority issues. They all should have corresponding issues in the library's issue tracker when we start working on them. The discussions about the usability of the library within the Toolkit should take place here.

• More straightforward customization of ReadWriters behavior - More straightforward customization of ReadWriters behaviour com-lihaoyi/upickle#486
• Easier way to make custom, combined Readers and Writers (e.g. sealed trait Value and classes MyInt, MyString) + Readers for untagged unions (based on fields)
• Address "If a field at serialization time has the same value as the default, uPickle leaves it out of the serialized blob" - make it configurable, add a default with that.
• Fix maximal number of successive inlines (32) exceeded on more than 32 case class params when deriving ReadWriter.
• Add custom configuration for toolkit (nulls, fields same as default)

[SethTisue]

is there anything here that's still a concern before Toolkit goes 1.0? cc @lihaoyi