v0.1.0: Omitted fields support

This release adds the Omitted() method to the Variable type, which allows the user to identify if a null JSON value was present as actual null or completely omitted from the JSON. This can be helpful in case the user requires the JSON to have some mandatory fields.

What's Changed

• Add omitted functionallity by @wneessen in #10

Full Changelog: v0.0.5...v0.1.0