Add native convenience functions to parse JSON and YAML

Native function tests crash on golang 1.7/osx.  Unclear if this is a
golang/cgo bug on osx, or jsonnet_cgo is doing something incorrectly.
Not critical, provided the golang 1.8 builds continue to work.

Fixes #12

Adds support for native functions

Add a flag for extvars

Minor README updates

- Add travis build status badge
- Update description of current status
- Add note about upstream golang OSX+cgo issue with <1.8.1

Build release binaries for osx

Add direct links to jsonnet tutorial and stdlib

Implement diff subcommand

Uses github.com/yudai/gojsondiff for the heavy lifting.

Implement delete subcommand

This removes all objects listed in config files (and dependents) -
effectively reversing an `update --create`.

Intended for short-lived "try this out; now clean up" workflows.

Fixes #14

Make the install commands more cut+pasteable

s/go install/go get/

Fix reading YAML files

Update README to mention pre-built release binaries

Add a README.md

Accept a wider range of jsonnet result structures

There is some variation in jsonnet "result" conventions.  This change
assumes the top level is a JSON object, and then walks down looking
for objects with `apiVersion` & `kind` fields.

While walking down, the current code will expand JSON arrays, and
object values.

In particular, this should correctly accept:
- single-value JSON files
- arrays (jsonnet --yaml-stream)
- "filename->object" objects (jsonnet --multi)

(Note that any v1.Lists encountered are still expanded in a
second-pass, as before)

Attempt to topologically sort resources before updating

The goal is to make a best-effort attempt at reducing the number of
"crash-restart" loops required to bring up a group of interdependent
resources.

The current implementation is very simple and just sorts into 3 tiers:
- Namespace, ThirdPartyResource, StorageClass
- everything else
- Pods or similar (Pod/Job/Deployment/DaemonSet/StatefulSet)

travis.yml: Build linux release builds using a musl/C++ toolchain

Add missing vendored library

govendor fetch github.com/emicklei/go-restful/swagger@v1.2

Rename backsplice -> ksonnet

Rename early and often.