Add default values.

[Wolftein]

Add a way to get a default value if the node does not exist.

Current:

name = node.containsKey("Name") ? node["Name"].as!string : "Default Value";

New

name = node["Name", "Default Value"].as!string;

[kiith-sa]

I'm not going to implement this (although should be easy to create a UFCS external method if you really want it).

Reasons:

• I don't like the idea of constructing and then unpacking a Node, because of performance but mainly because it will complicate eventual pure/@safe annotations I'm adding as related issues are fixed in Phobos.
• I want the API to be more explicit than implicit (make it obvious what you're doing by using containsKey() vs maybe reading the value or maybe not reading it.
• There's a simple (although more verbose) pattern to achieve the same thing. First declare all variables you're about to read initialized with their defaults, then read all of them in a try/catch block, and silently ignore a throw.
• And I like the idea that a missing value throws by default (with default values, I would not get that throw; I'd have to explicitly check for the error instead (yeah, this is an opposite side of the implicit/explicit thing))

Yes, I realize most of these are subjective and can be argued for both sides.

Sorry for the (massive) delay.