Option to ignore failed operations #57

Would be useful with an option to ignore operations that cannot be applied on the target.

Suggestion:

patch.ApplyTo(backendModel, ignoreErrors: true);

or

services
    .AddMvc()
    .AddJsonMergePatch(o => o.IgnoreErrors = true)

Not sure IgnoreErrors is the best name.

This is useful when the payload contains too many fields. In my specific scenario I'm dealing with polymorphism and the payload has a type field that is not present on the target model.
But it gets worse :( the payload doesn't care about polymorphism so it'll just send null values when a field isn't relevant. This isn't ideal, but it's what I have to deal with :/

Hope you'll consider it