Update YouTube.cs

Implemented a few useful methods.
Merge pull request #6 from abjerner/patch-1

Update YouTube.cs
Add in umbraco test site credentials
Update YouTube.cs

Added some error checking and methods for getting thumbnail URLs.
Update README.md
Merge pull request #8 from abjerner/patch-1

Update YouTube.cs
Merge pull request #9 from abjerner/patch-2

Update README.md
Update Dates.cs

The ToUnixTime() method assumed the current timezone as GMT 0. The method now corrently converts the specified DateTime to universal time. The start of the UNIX epoch is now also based on UTC rather than the current timezone.
Merge pull request #10 from abjerner/patch-3

Update Dates.cs
Merge remote-tracking branch 'upstream/master'

Conflicts:
	ExtensionMethods/YouTube.cs
Removed GetYouTubeId Method from YouTube.cs as abjerner wrote it already.
Added InvertCase method to String.cs. Removed GetYouTubeId method as it is duplicate and minor modifiction in some methods.