Feature/#61 extend each

[jolidog]

Fixes #61 #37 #67

Hi @LukyVj I needed the functionality requested in the previous issues so went ahead and wrote the code.

I'm using the :nth-child(3n + 1) method, where 1 indicates the offset.

Also updated the documentation and made every() an actual alias of each() with a different default starting point. They now use the same logic.

Caveats

• By providing a default 0 we garante we don't break anyones use of the each() mixin
• By providing a default of 1 to every() it might break the current use so it's your call to keep them different or not.

[LukyVj]

Oops I'm sorry, I didn't had time to check before. I'll take care of it this weekend.

Thanks a lot for this!

[jolidog]

@LukyVj I'm assuming you haven't had time to review. Ping me if you need.

[LukyVj]

Could you please fix the conflict :) ? And I'm mergin it