Add auto stringify on filters for non primative types

[zailleh]

It would be really nice if I could do this:
Resource.where({ createdAt: { lte: new Date() } }).all()

But in order for spraypaint to recognise the filter, I need to stringify it first, otherwise it silently ignores it.
Resource.where({ createdAt: { lte: new Date().toUTCString() } }).all()