Add support for block comments

[andrewmherren]

This is just a place holder issue to add support for block comments like /* comment */

This should be fairly straight forward with ast parser since the comments array includes comments of both type CommentLine and CommentBlock however this will be challenging as support is added for languages for which the ast parser cannot be used.

[idoo]

@Bogdan-Lyashenko @andrewmherren could you take a look to #82 ?