Signed-off-by: Jessica Yao <jessica@heptio.com>

Remove link to releases page

ksonnet.next isn't released yet. This message remained as a port from
the original README file in the kubecfg project.

Rename binary to 'ks';  rename 'kubecfg' references to 'ksonnet'

Introduce namespace to environments

Environments currently have the concept of a server URI, but it is
ambiguous which cluster namespace to use.

This commit will introduce the concept of namespaces to the env
commands.

For example,
`kubecfg env add staging http://mock-staging-uri \
 --namespace=staging-namespace`
`kubecfg env set staging --namespace=staging-namespace`

The default environment will use the namespace of the default context.

This commit will also update commands that take the <env> arg such as
`apply` to make use of the env namespace, if specified.

Environment base.libsonnet and overrides

Commands that take `env` as a param currently expand all files in the
`components` directory. This is no longer necessary with the
introduction of `base.libsonnet` and the per-environment override
`<env>.jsonnet` file.

This commit will simply expand the single `<env>.jsonnet` file (which
will implicitly expand all component files). The case of running
`ksonnet apply default`, is equivalent to running `ksonnet apply -f
environments/default/default.jsonnet`.

This commit will generate an "<env-name>.jsonnet" file when an
environment is created.

For example, the default environment would have the following tree
structure:
├── environments
│   ├── base.libsonnet
│   └── default
│       ├── .metadata
│       │   ├── k.libsonnet
│       │   ├── k8s.libsonnet
│       │   └── swagger.json
│       ├── default.jsonnet
│       └── spec.json

The goal of this file is to allow users to extend on base.libsonnet on a
per-environment basis to allow for custom overrides, such as replica
count.

base.libsonnet is a generated file that exists at the root of the
environments directory. This file is generated for all ksonnet projects.
The main goal of this file is to import all components in the components
directory, so that environments are able to easily extend / override any
one of these components in a modular structure.

This change simply hides the environment metadata details that we do not
want users directly modifying into a .metadata folder.

Remove unnecessary param from defaultNamespace()

The `clientConfig` param currently being passed is not needed, because
it exists as a package level var in root. It also makes little sense to
pass a custom `clientConfig` because if `overrides.Context.Namespace` is
populated, the namespace that is returned is configured as an override
in the package level `clientConfig` and not the `clientConfig` in the
param.

Remove client-go flags from commands that don't use

Add arg length constraint to commands

Construct base components Obj

In order to support environment heirarchy, we need to be able to
reference all components. This commit will implement component imports
as k-v pairs ex: foo: "import/foo.jsonnet" as a Jsonnet object. This
jsonnet object will then be assigned as an ExtCode so that it can be
referenced by a base.libsonnet file which environments can build /
override upon.

Fix 'env set' where --name flag is not specified

There is a bug where if --name is not passed during env set, an error is
thrown due to failed validation checking on an empty name. This commit
fixes this bug.

Add combination deployment/service system prototype

Implement 'prototype preview'

Currently the command 'prototype use' expands a prototype and prints to
stdout. This is useful, but most of the time, users want to simply dump
the result in 'components/'

This command implements this print-to-stdout behavior in a new command,
'prototype-preview', and reimplements 'prototype use' to drop the
expanded prototype into 'components/'.

The new form of this command is:

  ksonnet prototype use <prototype-name> <component-name> [type] [flags]

So, for example, a command like:

  ksonnet prototype use deployment nginx-depl [...]

would expand the 'deployment' prototype, and place it in
'components/nginx-depl.jsonnet' (since Jsonnet is the default template
expansion). Alternatively, something like this:

  ksonnet prototype use deployment nginx-depl yaml [...]

would expand the prototype and place it in 'components/nginx-depl.yaml'
(assuming that there is a YAML version of this template.

Currently `metadata.isValidName` will admit names that should be invalid
(e.g., names with spaces, leading '/' characters) and not admit names
that should be valid (e.g., names with '.' characters inside).

This commit moves this function into `metadata/interface.go` and hardens
it against these constraints.

Add help docs for `delete`

Fixes #132.

Add example to the service prototype's documentation

Add `prototype list` command

Fixes #108.

The `prototype list` command lists all known prototypes. It is
functionally equivalent to a `prototype search` that returns all
prototypes.

Cause `init` to generate env using current-context

When we run `init`, currently we generate a simple environment called
'default' with no URI. A better idea is to generate the URI from the
current context of the active kubeconfig file, if it exists.

Fix improper elision of -J flags

Set default log level to 'Info'