Add a rule to enforce maximum comment width

[gajus]

Add a rule that allows to set a variable maximum width of comment.

This rule is designed to prevent silly long comments, e.g.

/**
 * aaabbbcccaaabbbcccaaabbbcccaaabbbcccaaabbbcccaaabbbcccaaabbbcccaaabbbcccaaabbbcccaaabbbcccaaabbbccc
 */

That (depending on the text editor) require that user scrolls the window horizontally to read the entire comment.

Have a sane default, e.g. 70 to encourage consistent width across projects that use JSCS.

Do not forget to consider fullwidth characters. I suggest to use string-width.