Breaking apart schema generation code

[salotz]

Originally a conversation from: python-attrs/cattrs#397

I would propose that this code be broken out into its own repo distinct from uapi and cattrs.

While I do have an interest in uapi I have other uses for schema generation/loading into Python for which this code is very useful for on its own.

At this time I am going to vendor in the relevant code and continue to make modifications and updates to be utilized in a generic way. I would very much like to contribute back but would like to get @Tinche 's input (and others like @AdrianSosic that expressed interest) before putting in the effort completely for a new package.

I don't have enough time at this moment to make a full fledged package of this, but will use it in our internal product to mature the implementation some more. Ideally, I'd like to have some other projects utilizing it to help with maintenance and the overall ecosystem.

[salotz]

A banal concern but internally I am using the code name scattrs for this module. And will propose this as the name for it going forward.

I considered schattrs but it doesn't look nice.

[Tinche]

I'm totally on board with this becoming a separate package when it matures a little, definitely.