Support for array of types in JSON schema

[florianreinhart]

The following is a valid schema, but currently unsupported by fast-json-stringify:

{
    "type": "object",
    "properties": {
      "stringOrNumber": {"type": ["string", "number"], "maxLength": 10}
    }
}

[mcollina]

Definitely! Would you like to send a PR?

[florianreinhart]

I am already working on it.

We need to conditionally require ajv like it is done for anyOf in the hasAnyOf function. The hard part is to figure out if the schema includes any type arrays.