- Add message:  Creating a new app 'foo' at path '/path/to/foo'
- On success, add message:  ksonnet app successfully created! Next, try
  creating a component with `ks generate`
- On failure, provide suggestions for the user.
- Make note that the context is retrieved from the kubeconfig file at
  the environment variable $KUBECONFIG

Rename <env>.jsonnet file to main.jsonnet

Fix `nil` dereference error in #129

In line 161 of `root.go`, we're failing to check whether a cluster in
the $KUBECONFIG clusters array exists before using it. This will cause a
`nil` dereference error.

Transition system templates to beta.3

Currently, there are limitations around the file system we are using
that does not easily allow renaming of `us-west/prod` to `us-west`, or
vice versa - `us-west` to `us-west/prod`.

This commit will handle the logic to allow for that by moving the file
contents.

Remove command update

[docs] Very minor README edits

[docs] Fix ksonnet concept overview image + minor doc nits

Update is a deprecated command that was ported over from kubecfg. Since
ksonnet has not had any releases yet, it makes little sense to keep the
command.

[docs] Concepts Reference

First pass at CLI documentation formatting fixes

[docs] Update README

Currently, creating a `dev` environment will create a file
`dev.jsonnet`. Creating a `prod` environment will create a file
`prod.jsonnet`. This is a little more complex and prone to error than it
needs to be, especially when we are renaming environments. It will also
make this file easier to refer to in documentation if we give the file a
static name -- `main.jsonnet`.

Normalize environment server URL

Gracefully handle error when kubeconfig not present

YAML, JSON handling for prototype commands

As part of the environments feature, we want to be able to deploy to a
specific cluster given the environment's URI. We cross-check against
kubecfg for this URI's location. For fail-safe comparison, we probably
want to normalize these URIs.

We decided that this would give the users too many options. We should
limit the documentation to Jsonnet.

[docs] Add autogenerated CLI reference

Implement `registry describe` and `dep describe`

The command `dep` currently broadly allows users to inspect, use, and
search for packages. Currently, however, the name `dep` suggests that
this functionality is scoped to dependencies. Consider, for example, the
command `dep list`. A user might reasonable expect this to list all
dependencies, rather than all packages, which is what it does. Another
example is `dep search`, which actually searches all known packages, not
all known dependencies.

Hence, this commit will rename this command to simply be `pkg`.

This commit will partially resolve #38.

`registry list` and `registry describe` were designed to behave very
similarly to `prototype list` and `prototype describe`. The former
command is self-explanatory, and the second does displays some
documentation about the object in question.

This commit will implement these commands per the spec, and is a partial
fix to #38.

 Add `--help` flag to `generate` and `prototype use`

When `generate` was first implemented, we made a conscious decision to
not include the `--help` flag, so that we would not accidentally break
templates with a parameter called `help`.

But, this is unintuitive for users who want to use the `--help` flag, so
in this commit we will print the help message if (1) there is a single
command argument, and (2) it is either `--help` or `-h`.

Fixes #21.