vyconf doesn't require oasis.

This is useful in the parser and possibly other code that creates
nodes from scratch.

It will be used for migrating configs if incompatible syntax change is made.

Subject to improvement and extension to cover more cases.

It's problematic for multiple reasons:
1. It's plaintext and is hard to verify
2. If it's wrong,...

They are trivial to add with printf when needed anyway, and this function
is useful for generatin...

to make things simpler for callers.

Add toml and fileutils to the build dependencies information in the README

What's bad is that right now way too many things are aware of the nature of external validators,
...

It's the only type it exports.

Use of the Result module from a compatibility library came from using Yojson
for config parsing, ...

Add an example of the file too.

Related to T210.

If we ever modify those files, we'll remove them from .gitignore of course.

The correct way to write sequences with expressions of type other than unit
is to use the ignore...

Yojson now uses the Result.result type for its decoding functions
instead of polymorphic variants.

Restrict the Message module interface to the message types and decoder function.

It shall not be used by Config_tree, so there is no reason to keep it there.

Situations when two lists are the same and when they don't have a common
part become indistinguis...

input from the reference tree anyway.

Make value modification functions behaviour multi-value no...

That was not so much of a bad idea after all.

This is important for decision is set should add or replace a value.

Mainly for quickly getting data from a reference tree.

Make insertion at the beginning default behaviour.
Implement insertion at the end.