Update download links in README.md from v2.4.0 to v2.4.1

fix typo: ' instead of `

fix(helm): reverted upgrade of imdario/mergo

    Reverted the version of mergo to a version that was known to work
    with both kubernetes and sprig.

    Closes #2376

Implements --repo flag to commands fetch, install, inspect, upgrade

chore(tiller): bump Sprig to 2.11.0

This adds the `merge` function, among other things.

fix(releaseutil): remove newline on SplitManifests

fixes #2158

fix(create): incorrect URL in default NOTES.txt

Return as not ready if it new RS is nil

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