Streamline API for property access

[trogmaniac]

Use the [] operator to shorten the code. E.g. instead of:

auto width = resolution->GetProperty("width")->GetValueNumber();

i would prefer something short(er) like:

auto width = resolution["width"].AsInt();

This was just a single example, this should work where ever possible.

[mtangoo]

I see. It is common in many languages and so it will be great to have it.
Also I like that naming. I think I will deprecate both GetValueXX and add []/ASXX

[mtangoo]

@trogmaniac would you mind making PR with those additions?