Signed-off-by: Matt Butcher <matt.butcher@microsoft.com>

Removes Time, Namespace, and Revision from being exposed to templates to
make template rendering discrete and repeatable.

Signed-off-by: xianlubird <xianlubird@gmail.com>

docs(helm): Added kubeVersion to documentation and examples.
Adjusted wording for the Chart.kubeVersion description
Removing redundant wording for Chart.kubeVersion description

This adds support for changing '<CHARTNAME>'
occurances in starter chart to the destination
chart name

Each maintainer can have an optional URL. There are seceral use
cases for providing a URL instead of an email address:
- The case where a maintainer wants to hide their email address
  behind a webform for personal security
- When the maintainer is an organization and feedback should
  go to an issue queue

This change:
- Adds the proto field for url
- Updates the generated files for the chart proto
- Includes linting for the url
- Updates the docs to include the url

Closes #3056

There must be at least one subchart or template file, therefore the `charts` and `templates` directories are not strictly optional.

Unsupported value: "alwaysPull": supported values: Always, IfNotPresent, Never

Updating docs to prioritize `requirements.yaml` over `charts/` directory.

As `requirements.yaml` is the recommended strategy, let's document that first to make sure no one jumps the gun and goes ahead to implement manual deps via `charts/` just because they didn't read the whole section.

Remove incorrect statements in charts.md about nested globals not being allowed.

This provides the Chart.yaml field `tillerVersion`, which is a semver
range. It allows users to choose to constrain a chart to a specific
version.

The reason for this is that we keep introducing new template functions,
but we have no way of saying "this chart will only work with Tiller
newer than...".

The check on version is _only_ done on Tiller. The client does not check
at all, since it does not do any template expansion on its own.

Fix codefences and nits in charts.md. Correct whitespace in charts. Add clarity to description of ImportValues requirements field.

The WordPress community and especially the WordPress foundation
strongly prefer the use of WordPress, with the capital P.

Adds the `required` function in enginge.go to support required
properties in values.yml. When a chart developer wishes to specify
intent in requiring a value, they can use this function to declare
an error message that gets returned when chart rendering fails
when a required value is not present in values.yml.

Closes #1580

This provides a simple field to expose the version of the application
contained in a chart.

Closes #2036