Adds htmlmin; builds index file.

More work on tha build system

- Actually uses data to build the index page
- Minifies HTML
- Compiles files to the public directory

====

##### To test

- Copy the contents of [this gist](https://gist.github.com/jmeas/cec06ad14502f9e593bf) into a file `data/index.json`
- Run `grunt` from the command line
- Start a simple server (such as [node-static](https://github.com/cloudhead/node-static#command-line-interface)) from the public directory
  `npm install -g node-static && cd public && static`
- Navigate to `http://127.0.0.1:8080/`

It should work! :birthday: