This provides support for "global" variables. It does this by
declaring "global" to be a special namespace. It then copies this
namespace into every subchart, coalescing it into any "global"
namespace found there.

The net result is that if "global.foo" is set in the YAML file, it
will be available to every chart/subchart as ".global.foo" regardless of
where that chart is in the subchart tree.