logging Object becomes "[object Object]"

[DaxChen]

when logging structured data, for example:

log.warn({ foo: 123 });

It shows as:

logs: [{message: "test warn [object Object]", level: "warn", logger: "",…}]

console shows normal though.

Can you call JSON.stringify on either each argument or the whole args?
Or even let users define format function? (current format function gets "[object Object]" already...)

[kutuluk]

log.warn('%o', { foo: 123 });

or

log.warn('%j', { foo: 123 });