New encoding layer

[sagikazarmark]

Expose a new encoding abstraction layer. It allows users to bring their own encoding logic into Viper.

It also allows moving some of the less used formats (HCL, INI, Java properties) out of the core.

[sagikazarmark]

@skitt @andig could use a pair of extra eyes on this.

[andig]

It also allows moving some of the less used formats (HCL, INI, Java properties) out of the core.

@sagikazarmark this still does not remove the go.mod dependencies, or does it?

[sagikazarmark]

@andig not yet. This is just the first step to still allow using those libraries once they are removed.

[sagikazarmark]

I think this is ready