lineman-blog postinstall setup

![screen shot 2014-04-12 at 11 28 18 pm](https://cloud.githubusercontent.com/assets/69559/2688657/2b24c3e2-c2bc-11e3-802e-4b48747be968.png)

I'm opening this as a work in progress, I'd like to pair with someone on a few things to improve this code but also to get the discussion going about how this could be useful. Some design goals for this PR are:

- let users easily generate a new blog `lineman new my-blog && npm install lineman-blog --save-dev`
- delete lineman-blog-template
- figure out a way to simplify and normalize sample file generation
- figure out the right way to delete directories and files from the archetype that aren't needed by a specific plugin like this

## Testing

1. Generate a new project with `lineman new my-blog`
2. Modify the new projects pacakage.json and add:

```json
  "devDependencies": {
    "lineman-blog" : "git://github.com/linemanjs/lineman-blog.git#postinstall-stuffs"
  },
```

3. `npm install` to see the script in action

@searls @jasonkarns @jayharris to comment please :)