Add support for AMD-style modules

Hi,

I needed to generate AMD-style modules using Jison, but this Grunt task was unable to. So I have added support.

The real change is in going from `parser.Parser` to `parser.Generator` in the task-file. And then I updated the task to use the Options-API from Grunt, so you can set default options for task, and specific options for each target.

So now it's

```
jison: {
  options: {
    moduleType: 'js' /* for all targets */
  },
  target1: {
    files: { 'output.js': 'input.jison' }
  },
  target2: {
    options: {
      moduleType: 'amd' /* only for this target */
    }
    files: { 'output.amd.js': 'input.jison' }
  }
}
```

I've updated the README.md to reflect the changes, and I have updated the tests to test the new behaviour.

Because JSHint has changed their default-settings between when this task was first created and now, I've also updated the `.jshintrc` file to no longer have `es5: true`, as this is the new default behaviour. 

Kind Regards
Morten