fix(*): handle unreleased versioning

Releases are locked to avoid parallel changes

fix(tiller): fix TOML panic

ref(getter): flatten the getter package tree

feat(helm): add service account flag to helm init

Add support for zsh to helm completion

This flattens the getter package tree, adds tests, and changes a little
bit of the terminology to follow Go idioms. This also makes much of the
getter API private to begin with. This will give us more flexibility in
the future.

Adds an `unreleased` flag to the version if not building from HEAD of a
tag. The compatibility check is bypassed if the client or server are
unreleased.

fixes #2110

helps with half of #2224

chore(ci): bump go 1.8.1

This fixes a TOML panic by replacing one parser library with another.
The older library did not gracefully handle reflection issues, and so
was prone to panic. The new one is not great, but it doesn't seem to
panic.

Closes #2271

Fail template execution if included template fails

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

fix(helm): fix style errors in pkg/environment

docs(chart_hooks): clarify hook execution order

fix(helm): return error when dependencies are missing

chore(*): cleanup unused travis and scripts

feat(*): update to latest gRPC and Protobuf

Add Git and Mercurial to build prerequisites

This just adds a few comments where the style linter was complaining.

Closes: #2343

Closes #2234

This upgrades a warning to an error in cases where `requirements.yaml`
contains a requirement, but it's missing in charts/

This impacts install, upgrade, and package.

Closes #2209

fix(tiller): update tls client auth policy

Effectively, this switches us to gRPC's internal version 4. This is
compatible with protoc 3.2 and grpc-go 1.2.1.

Update Slack channels

Improve get script

Environment is supplied with release lock map which allows to lock a
release by name to make sure that update, rollback or uninstall aren't
running on one release at the same time.