This reverts a previous decision to only do shallow merges of globals.
It allows globals to be nested maps.

New properties are available to template developers.

Closes #1554

Templates can now access the non-template files in a chart by using
the '{{.Files}}' map inside of a template.

Relates to #950

This fixes a bug in which passed-in values files were not correctly
merged into the chart's default values YAML data. I believe it also
fixes some other prioritization bugs in values merging.

The existing unit test was wrong (see TestCoalesceValues). It is
fixed now. Also added more tests to simulate issue #971.

In the course of writing this, I removed some vestigial code as
mentioned in #920.

Closes #971
Closes #920

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.

This adds code to parse TOML files into Values maps. These can then
easily be passed into the template engine.

Included in this is support for TOML "tables", subsections of TOML
files. We will be using those to pass config data to dependent charts.