Add extension method option

[lfmundim]

Select type of issue

• Bug
• Feature request

If it's a feature request...

Please explain your request and why you'd like to see it in this service.
Currently to use the library we need to call the Zodiac class directly. C# enables us to use extension methods. This could make us simply call .GetZodiacSign() from a DateTime instance and have the code simpler and shorter.

// now
Zodiac.GetZodiacSignForDate(dateTime);

// suggested
dateTime.GetZodiacSign();

I could implement it :)