Help Updates

Beginning to update comment-based help and wiki pages to match each other (and be accurate for v3.0 usage.)
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Also, made Name parameters to Describe / Context / It explicitly of type [string] instead of the implied [object] type.
This avoids a bug which was allowing empty strings to be passed for names to these parameters, which doesn't play well with
the PesterState object.
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Merge pull request #190 from dlwyatt/HelpUpdates

Help updates
Update CHANGELOG.md