add "has" function (parent selector)#8

* CSS does not have a parent selector. * cheerio has [`has()`](https://github.com/cheeriojs/cheerio#has-selector---has-element-) selector. Since we want Surgeon to work across different environment (i.e. browser), we'd need to implement this on the Surgeon level. ## Use case Sometimes it is required to know whether an element has a descending element to know if it is the right element, e.g. http://www.mk2.com/salles/mk2-gambetta. To select all table rows that contain movie information, we can check if a table row includes information about the movie name. ```css #seances .l-mk2-tables .l-session-table .fiche-film-info::has(.fiche-film-title) ```