fix: infer - arrays should always accept null

[rafaeljusto]

When building the JSON schema for an array we should always allow "null" since any slice in Go can contain a nil value.

Resolves #48

[rafaeljusto]

This is another behaviour change, so I assume we would also need to wrap it around JSONSCHEMAGODEBUG? Should we keep the same typeschemasnull=1 flag value or use a different one?

[jba]

This is another behaviour change, so I assume we would also need to wrap it around JSONSCHEMAGODEBUG? Should we keep the same typeschemasnull=1 flag value or use a different one?

Yes. You can use the same flag value.

Also please update the README describing the env var and both effects of this flag.

[jba]

Actually not the README. doc.go at the bottom. Add a new section: # Controlling behavior changes.
Describe the env var and list the flag values using a dotted (unordered) list. Even though there's only one.

[rafaeljusto]

Done @jba ! Let me know if I should apply further changes. 🙂