Support multiple target formats

[dyst5422]

I recently found out about JSON Type Definition, which is not extensive as JSON Schema in its goals, but definitely similar. I think a big part of it is targeting code-generation for multiple languages (see https://jsontypedef.com/docs/)

Given the similarity, I figured the internal representation in this library prior to serializing into json schema would be sufficient for producing JSON Type Definitions, which can then be used for generating code in other languages.

Discuss!

[domoritz]

Could work. Have a look at #101 for some more discussion around future ideas for schema generators.