Prevent Choking on Pseudo Classes/Elements. Fixes #17

Rather than let the `NotImplementedException` bubble from CsQuery [here](https://github.com/jamietre/CsQuery/blob/30b56cf832ac3c4d09a30fe6a8164df819b57782/source/CsQuery/Engine/SelectorParser.cs#L135), we strip out pseudo classes/elements before processing. We also add a HTML comment to the output to say we've done so to (hopefully) avoid confusion.

Also realised I've been writing 'psuedo' everywhere. So corrected the typos too. <facepalm/>