docs: 🐛 Fixed all code examples (missing '), Rewrote upgrading Ob…

[cycle4passion]

Thanks for another great tool.

[CaptainCodeman]

Thanks for the PR

The only thing I would change is the "object upgrading" example. I don't think anyone should be adding an arbitrary property like this (the $settings.theme = 'system'; part), instead the idea was that it will save you having to manually add a property (which would normally have to include a check if it was undefined) and keep the default definitions together without any repetition, and the typing of settings (for this example) intact.

i.e. you just need to define the new initial default value and even if someone has already saved a version without it, it will be added, with no need for you to handle versions that didn't have it, so settings.theme would be set to 'system' without you having to do anything, regardless of whether it was previously persisted or not (most of the other libs end up returning undefined in this case)

Hope that makes sense :)