feat: allow reviving user types from saves without eval

[io-spectre]

It is quite common for authors to accept (or even require) save files for bug reports. Therefore we should allow authors to completely opt-out of executing arbitrary code on save load. This is implemented here by introducing Config.saves.isEvalEnabled (which currently defaults to true).

I've implemented a simple somewhat-more-explicit method for reviving user types which does not need eval-like powers by using a registry-based dispatch mechanism:¹

// Assume that you have a custom class named `Character` that you wish to
// register with the serializer. Note that the class doesn't need to be in the
// global scope for this to work.
class Character {
	static serialId = 'Character'; // unique identifier for this class, could also be a UUID
	constructor(data) {
		// initialize the instance with the given data...
	}
	// class implementation...
	toJSON() {
		return Serial.createRegisteredReviver(Character.serialId, /* own data chunk */);
	}
	// more class implementation...
}
// Register the `Character` class with the serializer.
Serial.registerUserType(Character.serialId, {
	revive : (data) => {
		return new Character(data);
	}
});

I'm open to bike-shedding and if I've violated some sort of style guide, please let me know. I'll fix it asap.

Resolves #390

Footnotes

1. The mechanism could be extended to automatically detect a registered serializer based on the prototype, etc. but I thought this minimal equivalent feature set to be less controversial. ↩

[io-spectre]

btw. why is there support for Infinity but not Number.NEGATIVE_INFINITY or Number.NaN?