Pass config to Comb constructor

You can now create new Comb instance and configure it at the same time.
To use one of predefined configs, pass its name:

    var comb = new Comb('zen'); // or `csscomb`, or `yandex`

To use custom config, pass its object:

    var comb = new Comb({ 'always-semicolon': true });
Make `new Comb()` and `configure()` chainable

You can now do things like:

    // Init, configure and process:
    var css = new Comb('csscomb').processFile('nani.scss');

    // Comb a file with one line of code:
    new Comb().configure({ 'always-semicolon': true }).processFile('panda.less');
Merge pull request #129 from csscomb/tg/102-chainable-methods

Pass config to `new Comb()` and make it chainable (#102)