Add nested parameters

Use nested parameters. For example:
Gruntfile.js:
    grunt.initConfig({

        htmlbuild: {
            dist: {
                src: 'index.html',
                ...
                options: {
                    ...
                    sections: {

                        animals: {
                            cat: 'cats/*.html',
                            cow: 'cows/*.html',
                            dog: 'dogs/*.html'
                        },
                        ...
                    },
                    ...
                }
            }
        },
    });

index.html:
…
<!-- build:section animals.cat -->
<!-- /build -->
…
Add multiple parameters

If parameter has sub-parameters, all files merge
Merge pull request #20 from Devoll/sub-parameters

Add sub-parameters