2.4.0 stopped installing development versions by default. This allows
the user to re-enable that support by setting --devel.

Closes #2407

* Adds update option to plugin command

Fixes issues/2385 - helm install silently updates the plugin, if it pre-existed

* Added tests for new methods for plugin update

* Updated docs

* Updated review comments :)

* Return error exit code when there is error

helps with half of #2224

Updated the 'helm completion' command to take in the shell
as a parameter. Currently acceptable options are 'bash' and
'zsh'. Also fixed the completions to work with zsh in a manner
similar to what kubectl does.

Also updated the docs to reflect this change.

Closes #2201

Rebase on kubernetes v1.6

gosimple seems to be eating all memory in CircleCI.  Testing disabling
the check to see if CI builds.

This change prevents downloading the same version as already installed.

`unbound variable` error occurs when docker-machine is not used.

This adds a hidden 'helm doc' command that generates documentation out
of the Helm help text.

Currently it can create:

- man pages for HELM(1)
- Markdown documentation
- bash autocompletions

Those are the three built-ins for Cobra.

The command is hidden so that it doesn't show up to the regular user,
since this is really a specialized task. It has the advantage of making
it trivially easy to install man pages and bash completion at installation time.

shasum is not on many platforms (like centos), use openssl instead.

gometalinter has moved to versioned releases. The latest of the v1
major versioned releases can be retrieved through pkg.in. This
change moves gometalinter use to the latest v1 release.

Downloading of charts and helm itself happened over http. This
change moves to use https as that is available with valid certs.

A bucket name in the path can be migrated to a custom k8s domain
name. This is in preperation for that.

This adds 'scripts/get`, which is a bash script for fetching and
installing the Helm client. It has the following features:

- It uses the GitHub API to discover the latest release
- It downloads the SHA256 checksum and verifies the binary using it
- It does basic tests on the installation

Attempt for build speed record

Running in parallel will crash a circle ci node. Disabling until we can
build in some safeguards.