Making service.json optional, by default we will also look for a package.json

* ndm now falls back to package.json, if it can't find a service.json file.
* ndm looks for the `service`, `name`, `scripts` and `description` stanza in package.json.
* the `scripts.start` script will be used as the entry-point for the service wrappers.

Here's an example `ndm`ified package.json:

```
{
  "name": "thumbd",
  "version": "2.12.0",
  "directories": {
    "lib": "./lib",
    "bin": "./bin",
    "data": "./data"
  },
  "main": "./lib/index.js",
  "bin": {
    "thumbd": "./bin/thumbd.js"
  },
  "author": "Ben Coe <bencoe@gmail.com>",
  "engines": [
    "node"
  ],
  "scripts": {
    "test": "mocha -u bdd -R nyan",
    "start": "./bin/thumbd.js server"
  },
  "description": "Node.js/AWS/ImageMagick-based image thumbnailing service.",
  "keywords": [
    "image",
    "processing",
    "thumbnail",
    "imagemagick",
    "sqs"
  ],
  "service": {
    "env": {
      "AWS_REGION": {
        "default": "us-east-1",
        "description": "Default AWS region for SQS and S3"
      },
      "AWS_KEY": {
        "description": "What is your AWS Key (used by SQS and S3)"
      },
      "AWS_SECRET": {
        "description": "What is your AWS secret (used by SQS and S3)"
      },
      "BUCKET": {
        "description": "What S3 bucket would you like to store converted thumbnails in"
      },
      "TMP_DIR": {
        "default": "/tmp",
        "description": "what folder should thumbd use for temporary files"
      },
      "SQS_QUEUE": {
        "description": "What SQS queue should thumbd fetch work from"
      },
      "CONVERT_COMMAND": {
        "default": "/usr/local/bin/convert",
        "description": "Absolute path to ImageMagick bin"
      }
    }
  },
  "repository": {
    "type": "git",
    "url": "git://github.com/bcoe/thumbd.git"
  },
  "dependencies": {
    "knox": "~0.8.0",
    "aws-sdk": "~1.7.1",
    "underscore": "~1.4.2",
    "tmp": "~0.0.16",
    "optimist": "~0.3.4",
    "async": "~0.2.7",
    "sprintf-js": "0.0.7",
    "request": "~2.34.0"
  },
  "devDependencies": {
    "mocha": "~1.7.4",
    "sinon": "~1.6.0"
  }
}
```